U.S. patent number 9,891,828 [Application Number 15/206,412] was granted by the patent office on 2018-02-13 for tiered storage system, storage controller, and tiering control method.
This patent grant is currently assigned to KABUSHIKI KAISHA TOSHIBA, TOSHIBA SOLUTIONS CORPORATION. The grantee listed for this patent is Kabushiki Kaisha Toshiba, Toshiba Solutions Corporation. Invention is credited to Tomofumi Hasegawa.
United States Patent |
9,891,828 |
Hasegawa |
February 13, 2018 |
Tiered storage system, storage controller, and tiering control
method
Abstract
According to one embodiment, a tiered storage system includes a
first storage device, a second storage device and a storage
controller. The first and second storage devices are positioned as
an upper tier and a lower tier, respectively. The storage
controller transfers data of q physical extents in the second
storage device to q free physical extents in the first storage
device, when an access request from a host computer designates
access to one or more logical blocks including a first logical
block, the first logical block is included in a first logical
extent, and the first logical extent belongs to an extent group
including q logical extents to which the q physical extents are
allocated.
Inventors: |
Hasegawa; Tomofumi (Inagi,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Kabushiki Kaisha Toshiba
Toshiba Solutions Corporation |
Minato-ku
Kawasaki-shi |
N/A
N/A |
JP
JP |
|
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
(Minato-ku, JP)
TOSHIBA SOLUTIONS CORPORATION (Kawasaki-shi,
JP)
|
Family
ID: |
59351281 |
Appl.
No.: |
15/206,412 |
Filed: |
July 11, 2016 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20170269840 A1 |
Sep 21, 2017 |
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Foreign Application Priority Data
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Mar 16, 2016 [JP] |
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2016-052510 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G06F
3/0649 (20130101); G06F 3/0605 (20130101); G06F
3/0685 (20130101) |
Current International
Class: |
G06F
3/06 (20060101); G06F 12/08 (20160101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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5362145 |
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Dec 2013 |
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JP |
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2014-191398 |
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Oct 2014 |
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JP |
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WO 2014/155666 |
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Oct 2014 |
|
WO |
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WO 2015/162766 |
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Oct 2015 |
|
WO |
|
Primary Examiner: Dudek, Jr.; Edward J
Attorney, Agent or Firm: Oblon, McClelland, Maier &
Neustadt, L.L.P.
Claims
What is claimed is:
1. A tiered storage system comprising: a first storage device
including a first storage area having a plurality of physical
extents each including a first number of physical blocks, the first
storage device being positioned as an upper tier; a second storage
device including a second storage area having a plurality of
physical extents each including the first number of physical
blocks, the second storage device having a lower access speed than
the first storage device and being positioned as a lower tier; and
a storage controller which controls access to the first and second
storage devices, the storage controller comprising a configuration
management unit, an input/output controller, an input/output
management unit, a group management unit and a tiering controller,
wherein the configuration management unit constructs a logical unit
including a virtualized storage area comprising a plurality of
logical blocks each having a size identical to a size of each of
the physical blocks, and provides the logical unit to a host
computer which uses the tiered storage system; the input/output
controller reads data from the first or second storage device or
writes data to the first or second storage device in accordance
with an access request from the host computer; the input/output
management unit manages the virtualized storage area of the logical
unit as a storage area including a plurality of logical extents
each comprising the first number of logical blocks; the group
management unit manages a strength of linkage, associated with
access, of a respective combination of two different logical
extents included in the plurality of logical extents, based on a
degree of linkage which indicates a degree of successive access to
the respective combination, and manages, as extent groups, sets of
logical extents included in respective series of combinations that
mutually have a linkage relationship; and the tiering controller
transfers data of q physical extents, allocated to q logical
extents, in the second storage device to q free physical extents in
the first storage device, and changes q physical extents to be
allocated to the q logical extents from the q physical extents in
the second storage device to the q physical extents in the first
storage device, when the access request designates access to one or
more logical blocks including a first logical block, the first
logical block is included in a first logical extent, and the first
logical extent belongs to an extent group including the q logical
extents.
2. The tiered storage system of claim 1, wherein the input/output
management unit acquires an access statistical value indicating a
status of access to a respective one of the plurality of logical
extents; the group management unit determines an access statistical
value of a respective one of the extent groups, based on all
logical extents belonging to the respective extent group; and when
the number of free physical extents in the first storage device is
less by r than the q physical extents, the tiering controller
selects one or more logical extents belonging to none of the extent
groups, and/or one or more extent groups, in an ascending order of
first access statistical values and second access statistical
values, the one or more logical extents and/or the one or more
extent groups corresponding to at least r physical extents whose
data is to be transferred from the first storage device to the
second storage device, the first access statistical values being
access statistical values of logical extents which belong to none
of the extent groups and to which respective physical extents in
the first storage device are allocated, the second access
statistical values being access statistical values of extent groups
comprising sets of logical extents to which respective physical
extents in the first storage device are allocated; and the tiering
controller increases the number of free physical extents in the
first storage device by at least r, by transferring data of the at
least r physical extents in the first storage device, which are
allocated to the selected one or more logical extents and/or all
logical extents in the one or more extent groups, to the same
number of free physical extents in the second storage device as the
at least r physical extents in the first storage device.
3. The tiered storage system of claim 2, wherein the input/output
management unit determines, as the access statistical value of the
respective extent group, a maximum access statistical value or an
average statistic value of all logical extents belonging to the
respective extent group.
4. The tiered storage system of claim 2, wherein the input/output
management unit manages the status of access to the respective
logical extent, using the access statistical value and a last
access time of the respective logical extent; the group management
unit uses, as a last access time of the respective extent group, a
most recent access time of last access times of the logical extents
included in the respective extent group; and the tiering controller
increases a rank of selection of a selection candidate having an
older last access time when a plurality of selection candidates
having a same access statistical value exist.
5. The tiered storage system of claim 1, wherein the group
management unit detects a first extent group including a number of
logical extents exceeding a second number of logical extents, based
on the number of logical extents constituting a respective one of
the extent groups; the group management unit detects, in the first
extent group, a combination of a second logical extent and a third
logical extent, which has a minimum degree of linkage; and the
group management unit regroups the first extent group into a second
extent group including the second logical extent and a third extent
group including the third logical extent.
6. The tiered storage system of claim 5, wherein the group
management unit normalizes the degree of linkage of the respective
combination, using the minimum degree of linkage; and the group
management unit replaces a normalized minimum degree of linkage
with a value indicating no linkage.
7. The tiered storage system of claim 5, wherein the second number
is determined, based on the number of physical extents in the first
storage device, in which data can be arranged.
8. The tiered storage system of claim 5, wherein when p is an
integer not less than 2, the one or more logical blocks are p
logical blocks successively arranged in the logical unit, a part of
the p logical blocks is included in the first logical extent, and
another part of the p logical blocks is included in a fourth
logical extent, the group management unit increments a degree of
linkage of a combination of the first and fourth logical
extents.
9. The tiered storage system of claim 5, wherein the storage
controller further comprises an extent management table which holds
an extent group identifier, a preceding link extent identifier, a
succeeding link extent identifier, an access statistical value and
last access time data in association with a respective one of the
plurality of logical extents, the extent group identifier
indicating an extent group to which the respective logical extent
belongs, the preceding link extent identifier indicating a logical
extent which precedes the respective logical extent in order of
access, the succeeding link extent identifier indicating a logical
extent which succeeds the respective logical extent in order of
access, the access statistical value indicating a status of access
to the respective logical extent, the last access time data
indicating a last access time when the respective logical extent
was last accessed; the input/output management unit updates, in
accordance with the access request, an access statistical value and
last access time data associated with at least one logical extent
corresponding to an access range designated by the access request;
and the group management unit updates, in accordance with the
access request, an extent group identifier, a preceding link extent
identifier and a succeeding link extent identifier associated with
the at least one logical extent corresponding to the access range
designated by the access request.
10. The tiered storage system of claim 9, wherein the storage
controller further comprises a linkage management table which holds
the degree of linkage of the respective combination.
11. A storage controller used in a tiered storage system for
controlling access to a first storage device and a second storage
device included in the tiered storage system, the first storage
device including a first storage area having a plurality of
physical extents each including a first number of physical blocks,
the first storage device being positioned as an upper tier, the
second storage device including a second storage area having a
plurality of physical extents each including the first number of
physical blocks, the second storage device having a lower access
speed than the first storage device and being positioned as a lower
tier, the storage controller comprising: a configuration management
unit; an input/output controller; an input/output management unit;
a group management unit; and a tiering controller, wherein: the
configuration management unit constructs a logical unit including a
virtualized storage area comprising a plurality of logical blocks
each having a size identical to a size of each of the physical
blocks, and provides the logical unit to a host computer which uses
the tiered storage system; the input/output controller reads data
from the first or second storage device or writes data to the first
or second storage device in accordance with an access request from
the host computer; the input/output management unit manages the
virtualized storage area of the logical unit as a storage area
including a plurality of logical extents each comprising the first
number of logical blocks; the group management unit manages a
strength of linkage, associated with access, of a respective
combination of two different logical extents included in the
plurality of logical extents, based on a degree of linkage which
indicates a degree of successive access to the respective
combination, and manages, as extent groups, sets of logical extents
included in respective series of combinations that mutually have a
linkage relationship; and the tiering controller transfers data of
q physical extents, allocated to q logical extents, in the second
storage device to q free physical extents in the first storage
device, and changes q physical extents to be allocated to the q
logical extents from the q physical extents in the second storage
device to the q physical extents in the first storage device, when
the access request designates access to one or more logical blocks
including a first logical block, the first logical block is
included in a first logical extent, and the first logical extent
belongs to an extent group including the q logical extents to which
the q physical extents in the second storage device are
allocated.
12. The storage controller of claim 11, wherein the input/output
management unit acquires an access statistical value indicating a
status of access to a respective one of the plurality of logical
extents; the group management unit determines an access statistical
value of a respective one of the extent groups, based on all
logical extents belonging to the respective extent group; and when
the number of free physical extents in the first storage device is
less by r than the q physical extents, the tiering controller
selects one or more logical extents belonging to none of the extent
groups, and/or one or more extent groups, in an ascending order of
first access statistical values and second access statistical
values, the one or more logical extents and/or the one or more
extent groups corresponding to at least r physical extents whose
data is to be transferred from the first storage device to the
second storage device, the first access statistical values being
access statistical values of logical extents which belong to none
of the extent groups and to which respective physical extents in
the first storage device are allocated, the second access
statistical values being access statistical values of extent groups
comprising sets of logical extents to which respective physical
extents in the first storage device are allocated; and the tiering
controller increases the number of free physical extents in the
first storage device by at least r, by transferring data of the at
least r physical extents in the first storage device, which are
allocated to the selected one or more logical extents and/or all
logical extents in the one or more extent groups, to the same
number of free physical extents in the second storage device as the
at least r physical extents in the first storage device.
13. The storage controller of claim 12, wherein the input/output
management unit determines, as the access statistical value of the
respective extent group, a maximum access statistical value or an
average statistic value of all logical extents belonging to the
respective extent group.
14. The storage controller of claim 12, wherein the input/output
management unit manages the status of access to the respective
logical extent, using the access statistical value and a last
access time of the respective logical extent; the group management
unit uses, as a last access time of the respective extent group, a
most recent access time of last access times of the logical extents
included in the respective extent group; and the tiering controller
increases a rank of selection of a selection candidate having an
older last access time when a plurality of selection candidates
having a same access statistical value exist.
15. The storage controller of claim 11, wherein the group
management unit detects a first extent group including a number of
logical extents exceeding a second number of logical extents, based
on the number of logical extents constituting a respective one of
the extent groups; the group management unit detects, in the first
extent group, a combination of a second logical extent and a third
logical extent, which has a minimum degree of linkage; and the
group management unit regroups the first extent group into a second
extent group including the second logical extent and a third extent
group including the third logical extent.
16. The storage controller of claim 15, wherein the group
management unit normalizes the degree of linkage of the respective
combination, using the minimum degree of linkage; and the group
management unit replaces a normalized minimum degree of linkage
with a value indicating no linkage.
17. The storage controller of claim 15, wherein when p is an
integer not less than 2, the one or more logical blocks are p
logical blocks successively arranged in the logical unit, a part of
the p logical blocks is included in the first logical extent, and
another part of the p logical blocks is included in a fourth
logical extent, the group management unit increments a degree of
linkage of the first and fourth logical extents.
18. A method, in a storage controller which controls access to a
first storage device and a second storage device, for tiering, as
an upper tier and a lower tier, the first storage device and the
second storage device, respectively, the first storage device
including a first storage area having a plurality of physical
extents each including a first number of physical blocks, the
second storage device including a second storage area having a
plurality of physical extents each including the first number of
physical blocks, the second storage device having a lower access
speed than the first storage device, the storage controller
constructing a logical unit including a virtualized storage area
comprising a plurality of logical blocks each having a size
identical to a size of each of the physical blocks, and providing
the logical unit to a host computer which uses a tiered storage
system including the first and second storage devices, the method
comprising: reading data from the first or second storage device or
writing data to the first or second storage device in accordance
with an access request from the host computer; managing the
virtualized storage area of the logical unit as a storage area
including a plurality of logical extents each comprising the first
number of logical blocks; managing a strength of linkage,
associated with access, of a respective combination of two
different logical extents included in the plurality of logical
extents, based on a degree of linkage which indicates a degree of
successive access to the respective combination; managing, as
extent groups, sets of logical extents included in respective
series of combinations that mutually have a linkage relationship;
and transferring data of q physical extents, allocated to q logical
extents, in the second storage device to q free physical extents in
the first storage device, and changing q physical extents to be
allocated to the q logical extents from the q physical extents in
the second storage device to the q physical extents in the first
storage device, when the access request designates access to one or
more logical blocks including a first logical block, the first
logical block is included in a first logical extent, and the first
logical extent belongs to an extent group including the q logical
extents to which the q physical extents in the second storage
device are allocated.
19. The method of claim 18, further comprising: acquiring an access
statistical value indicating a status of access to a respective one
of the plurality of logical extents; determining an access
statistical value of a respective one of the extent groups, based
on all logical extents belonging to the respective extent group;
when the number of free physical extents in the first storage
device is less by r than the q physical extents, selecting one or
more logical extents belonging to none of the extent groups, and/or
one or more extent groups, in an ascending order of first access
statistical values and second access statistical values, the one or
more logical extents and/or the one or more extent groups
corresponding to at least r physical extents whose data is to be
transferred from the first storage device to the second storage
device, the first access statistical values being access
statistical values of logical extents which belong to none of the
extent groups and to which respective physical extents in the first
storage device are allocated, the second access statistical values
being access statistical values of extent groups comprising sets of
logical extents to which respective physical extents in the first
storage device are allocated; and increasing the number of free
physical extents in the first storage device by at least r, by
transferring data of the at least r physical extents in the first
storage device, which are allocated to the selected one or more
logical extents and/or all logical extents in the one or more
extent groups, to the same number of free physical extents in the
second storage device as the at least r physical extents in the
first storage device.
20. The method of claim 18, further comprising: detecting a first
extent group including a number of logical extents exceeding a
second number of logical extents, based on the number of logical
extents constituting a respective one of the extent groups;
detecting, in the first extent group, a combination of a second
logical extent and a third logical extent, which has a minimum
degree of linkage; and regrouping the first extent group into a
second extent group including the second logical extent and a third
extent group including the third logical extent.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority
from Japanese Patent Application No. 2016-052510, filed Mar. 16,
2016, the entire contents of which are incorporated herein by
reference.
FIELD
Embodiments described herein relate generally to a tiered storage
system, a storage controller, and a tiering control method.
BACKGROUND
A storage system comprising a first storage device and a second
storage device that have different access speeds has recently been
developed. Assume here that the access speed and storage capacity
of the first storage device are high and small, respectively, and
that the access speed and storage capacity of the second storage
device are lower and greater than those of the first storage
device, respectively. The storage system is realized by
hierarchically combining the first and second storage devices as
upper and lower tiers, respectively. This technique is also called
a storage tiering technique, and the storage system employing the
storage tiering technique is also called a tiered storage
system.
In the tiered storage system, tiers (storage devices) in which data
is to be arranged (stored) are determined/changed in accordance
with the characteristics of the data. More specifically, data
having a high access frequency is arranged in the upper tier (first
storage device), and data having a low access frequency is arranged
in the lower tier (second storage device). This arrangement
(namely, tiering) enables the tiered storage system to realize both
high performance and low cost.
In general, tiering in the tiered storage system is automatically
performed. For the automatic tiering, a storage controller
monitors, for example, an access status in the tiered storage
system data group by data group called an extent. The extent
generally has a size greater than the basic size (so-called block
size) for data management (data access). The status of access to
each extent is expressed by an access statistical value, such as
the number of accesses.
The storage controller performs, for example, periodically,
estimation associated with the access frequency of each extent,
based on the access statistical value thereof. Based on the
periodical estimation result, the storage controller transfers
(rearranges) data from the lower tier to the upper tier and/or vice
versa extent by extent. However, data transfer between the tiers
based on the periodical access frequency estimation will cause
significant overhead and require a large amount of time.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing an exemplary hardware
configuration of a computer system including a tiered storage
system according to an embodiment;
FIG. 2 is a block diagram mainly showing an exemplary functional
configuration of the storage controller shown in FIG. 1;
FIG. 3 is a diagram showing an exemplary relationship between
physical extents and physical blocks in the embodiment;
FIG. 4 is a diagram showing an exemplary relationship between
logical extents and logical blocks in the embodiment;
FIG. 5 is a diagram showing a data structure example of an address
translation table shown in FIG. 2;
FIG. 6 is a diagram showing a data structure example of an extent
management table shown in FIG. 2;
FIG. 7 is a diagram showing a data structure example of a link
management table shown in FIG. 2;
FIG. 8 is a flowchart showing an exemplary procedure of access
processing in the embodiment;
FIG. 9 is a flowchart showing an exemplary procedure of table
update processing included in the access processing of FIG. 8;
FIG. 10 is a flowchart showing an exemplary procedure of first
table update processing included in the table update processing of
FIG. 9;
FIG. 11 is a flowchart showing an exemplary procedure of second
table update processing included in the table update processing of
FIG. 9;
FIG. 12 is a diagram showing an example of the extent management
table obtained after the table update processing is executed in
response to a first access request;
FIG. 13 is a diagram showing an example of the link management
table obtained after the table update processing is executed in
response to the first access request;
FIG. 14 is a diagram showing an example of the extent management
table obtained after the table update processing is executed in
response to a second access request;
FIG. 15 is a diagram showing an example of the link management
table obtained after the table update processing is executed in
response to the second access request;
FIG. 16 is a diagram showing an example of the extent management
table obtained after the table update processing is executed in
response to a third access request;
FIG. 17 is a diagram showing an example of the link management
table obtained after the table update processing is executed in
response to the third access request;
FIG. 18 is a diagram showing an example of the extent management
table obtained after the table update processing is executed in
response to a fourth access request;
FIG. 19 is a diagram showing an example of the link management
table obtained after the table update processing is executed in
response to the fourth access request;
FIG. 20 is a flowchart showing an exemplary procedure of data
transfer source determination processing, which is included in the
access processing of FIG. 8;
FIG. 21 is a flowchart showing an exemplary procedure of free-area
securing processing included in the access processing of FIG.
8;
FIG. 22 is a flowchart showing an exemplary procedure of regrouping
processing according to a modification of the embodiment;
FIG. 23 is a diagram showing a configuration example of an expanded
extent group, and examples of linkage degrees of respective pairs
of successively accessed logical extents included in the expanded
extent group, along with an example of the link management
table;
FIG. 24 is a diagram showing, for comparison, examples of the link
management table obtained before and after a second preprocess in
the modification;
FIG. 25 is a diagram showing, for comparison, examples of the link
management table obtained before and after a third preprocess in
the modification; and
FIG. 26 is a diagram showing, an example of the link management
table obtained immediately after the third preprocess, and showing,
for comparison, examples of extent groups obtained before and after
the regrouping.
DETAILED DESCRIPTION
Various embodiments will be described hereinafter with reference to
the accompanying drawings.
In general, in accordance with one embodiment, a tiered storage
system includes a first storage device, a second storage device and
a storage controller. The first storage device includes a first
storage area having a plurality of physical extents each including
a first number of physical blocks, and is positioned as an upper
tier. The second storage device includes a second storage area
having a plurality of physical extents each including the first
number of physical blocks. The second storage device has a lower
access speed than the first storage device and is positioned as a
lower tier. The storage controller controls access to the first and
second storage devices, and includes a configuration management
unit, an input/output controller, an input/output management unit,
a group management unit and a tiering controller. The configuration
management unit constructs a logical unit including a virtualized
storage area having a plurality of logical blocks each having a
size identical to a size of each of the physical blocks, and
provides the logical unit to a host computer which uses the tiered
storage system. The input/output controller reads data from the
first or second storage device or writes data to the first or
second storage device in accordance with an access request from the
host computer. The input/output management unit manages the
virtualized storage area of the logical unit as a storage area
including a plurality of logical extents each having the first
number of logical blocks. The group management unit manages a
strength of linkage, associated with access, of a respective pair
of different logical extents included in the plurality of logical
extents, based on a corresponding degree of linkage which indicates
a degree of successive access to the respective pair of logical
extents, and manages, as extent groups, sets of logical extents
included in respective series of combinations that mutually have a
linkage relationship. The tiering controller transfers data of q
physical extents, allocated to q logical extents, in the second
storage device to q free physical extents in the first storage
device, and changes q physical extents to be allocated to the q
logical extents from the q physical extents in the second storage
device to the q physical extents in the first storage device, when
the access request designates access to one or more logical blocks
including a first logical block, the first logical block is
included in a first logical extent, and the first logical extent
belongs to an extent group including the q logical extents to which
the q physical extents in the second storage device are
allocated.
FIG. 1 is a block diagram showing an exemplary hardware
configuration of a computer system including a tiered storage
system according to an embodiment. The computer system shown in
FIG. 1 includes a tiered storage system 10 and a host computer
(hereinafter, referred to as a host) 20. That is, the computer
system includes a single host. However, the computer system may
include a plurality of hosts.
The host 20 uses, as its own external storage device, a logical
unit provided by the tiered storage system 10. The logical unit is
also called a logical disk or a logical volume, and includes a
virtualized storage area (namely, a logical storage area). The host
20 is connected to the tiered storage system 10 (more specifically,
a storage controller 13 in the tiered storage system 10) through,
for example, a host interface bus 30. In the embodiment, the host
interface bus 30 is Fibre Channel (FC). However, the host interface
bus 30 may be an interface bus other than FC, such as Small
Computer System Interface (SCSI), Serial Attached SCSI (SAS),
Internet SCSI (iSCSI), Ethernet (registered trademark) or Serial AT
Attachment (SATA). Moreover, the host 20 may be connected to the
tiered storage system 10 through a network, such as a storage area
network (SAN), the Internet, or an intranet.
The host 20 is a physical computer, such as a server or a client
personal computer. Within the host 20, an application program
operates for accessing data in the logical unit provided by the
tiered storage system 10. According to this application program,
the host 20 uses the tiered storage system 10 through the host
interface bus 30.
The tiered storage system 10 includes a high-speed storage device
(first storage device) 11, a low-speed storage device (second
storage device) 12 and the storage controller 13. The high-speed
storage device 11 and the low-speed storage device 12 are connected
to the storage controller 13 through a storage interface bus 14. In
the embodiment, the storage interface bus 14 is Fibre Channel (FC).
However, the storage interface bus 14 may be an interface bus other
than the FC, like the host interface bus 30.
The high-speed storage device 11 includes, for example, a single
solid-state drive (SSD) that is compatible with a hard disk drive
(HDD), and has a higher access speed than the HDD (that is,
superior thereto in access performance). In contrast, the low-speed
storage device 12 includes, for example, a single HDD.
Thus, in the embodiment, the low-speed storage device 12 is lower
in access speed than the high-speed storage device 11 (that is,
inferior thereto in access performance). In contrast, assume that
the storage capacity of the low-speed storage device 12 is greater
than that of the high-speed storage device 11. In the embodiment,
the high-speed storage device 11 is used as a storage device as an
upper tier (a high-speed tier=a first tier), and the low-speed
storage device 12 is used as a storage device as a lower tier (a
low-speed tier=a second tier). The tiered storage system 10 may
also include a storage device (as a third tier) lower in speed than
the low-speed storage device 12.
The high-speed storage device 11 may be a flash array storage
device with a flash memory, or a storage device called an all flash
array, unlike the embodiment. Similarly, the low-speed storage
device 12 may be a storage device of an array configuration
including a plurality of HDDs.
Alternatively, the high-speed storage device 11 may include a
high-speed HDD, such as an HDD for FC, and the low-speed storage
device 12 may include a low-speed HDD, such as an HDD for SATA.
Further, the low-speed storage device 12 may be an optical disk
drive, such as a Blu-ray disk (registered trademark) drive or a DVD
(registered trademark) drive, or a tape device. If the tape device
is used as the low-speed storage device 12, the optical disk drive
may be used as the high-speed storage device 11.
The storage controller 13 receives, from the host 20, a request
(input/output request) of access (read access or write access)
using a logical address, and executes the requested access
(input/output). For the execution of the access, the storage
controller 13 translates a logical address into a physical address,
using a well-known address translation function. The logical
address indicates an address in the logical unit. The physical
address indicates the physical position of a storage area that is
included in the high-speed storage device 11 or the low-speed
storage device 12, and is associated with the logical address. The
storage controller 13 accesses the high-speed storage device 11 or
the low-speed storage device 12, based on the physical address.
The storage controller 13 includes a host interface controller
(hereinafter, referred to as an HIF controller) 131, a storage
interface controller (hereinafter, referred to as an SIF
controller) 132, a memory 133, a local HDD 134 and a CPU 135.
The HIF controller 131 controls data transfer (a data transfer
protocol) between the HIF controller 131 and the host 20. The HIF
controller 131 receives an access request from the host, and
replies a response to the access request. The access request
designates a data read from or a data write to the logical unit
(namely, access to the logical unit). Upon receiving the access
request from the host 20, the HIF controller 131 transmits the
access request to the CPU 135. The CPU 135 having received the
access request processes the access request.
The SIF controller 132 receives, from the CPU 135, an access
command (more specifically, a read command or a write command to
the high-speed storage device 11 or the low-speed storage device
12) corresponding to the access request received by the CPU 135
from the host 20. The SIF controller 132 accesses the high-speed
storage device 11 or the low-speed storage device 12 in accordance
with the received access command.
The memory 133 is a rewritable volatile memory, such as a DRAM. A
part of the storage area of the memory 133 is used to store at
least a part of a control program loaded from the local HDD 134.
Another part of the storage area of the memory 133 is used to store
an address translation table 1331, an extent management table 1332
and a link management table 1333 loaded from the local HDD 134
(FIG. 2).
The local HDD 134 stores the control program. The CPU 135 loads at
least a part of the control program, stored in the local HDD 134,
into the memory 133 by executing an initial program loader (IPL)
when the storage controller 13 is started. The IPL is stored in a
nonvolatile memory, such as a ROM or a flash ROM.
The CPU 135 is a processor such as a microprocessor. The CPU 135
functions as a configuration management unit 1351, an input/output
(I/O) controller 1352, an input/output (I/O) management unit 1353,
a group management unit 1354 and a tiering controller 1355 (FIG. 2)
in accordance with the control program loaded into the memory 133.
That is, the CPU 135 controls the whole tiered storage system 10 by
executing the control program stored in the memory 133.
In the embodiment, the storage controller 13 is provided
independently of the host 20 as shown in FIG. 1. However, the
storage controller 13 may be built in the host 20. In this case,
the storage controller 13 (more specifically, the function of the
storage controller 13) may be realized using a part of the function
of the operating system (OS) of the host 20.
Alternatively, the storage controller 13 may be incorporated in a
card that is used, inserted in the card slot of the host 20. Yet
alternatively, a part of the storage controller 13 may be built in
the host 20, and the remaining part of the storage controller 13
may be incorporated in the card. Further, the host 20, the storage
controller 13, and part of or the entire high-speed and low-speed
storage devices 11 and 12 may be housed in a housing.
FIG. 2 is a block diagram mainly showing an exemplary functional
configuration of the storage controller 13 shown in FIG. 1. The
storage controller 13 includes the configuration management unit
1351, the I/O controller 1352, the I/O management unit 1353, the
group management unit 1354 and the tiering controller 1355. At
least the configuration management unit 1351, I/O controller 1352,
the I/O management unit 1353, the group management unit 1354, or
the tiering controller 1355 may be realized by hardware.
The configuration management unit 1351 manages the storage
configuration of the tiered storage system 10. This configuration
management includes constructing the logical unit and proving the
host 20 with the logical unit, based on the storage areas of the
high-speed storage device 11 and the low-speed storage device 12.
In the embodiment, the storage area (logical storage area) of the
logical unit is divided into small areas of a certain size called
logical blocks for managing the logical unit. That is, the logical
unit includes a plurality of logical blocks.
In contrast, the storage areas (physical storage areas) of the
high-speed storage device 11 and the low-speed storage device 12
are each divided into areas, called physical extents, having a size
greater than that of the logical block. Each physical extent is
further divided into small areas having the same size as the
logical block and each called a physical block. That is, the
storage areas of the high-speed storage device 11 and the low-speed
storage device 12 each include a plurality of physics extents, and
each physical extent includes a certain number (first number) of
sequential physical blocks.
In the embodiment, the storage area of the logical unit is also
divided into areas that are called logical extents, and each have
the same size as the physical extent. That is, the storage area of
the logical unit also includes a plurality of logical extents. Each
logical extent includes the same number (namely, the first number)
of logical blocks as that of the physical blocks. Accordingly, the
boundary of each logical extent coincides with the boundary of a
logical block.
The size (extent size) of each of the physical extent and the
logical extent is, for example, 4 Kbytes (KB), i.e., 4,096 bytes
(B). The size (block size) of each of the physical block and the
logical block is, for example, 512 bytes (B). That is, the first
number is 8, and each physical extent (logical extent) includes 8
physical blocks (8 logical blocks). However, the extent size and
the block size are not limited to 4 KB and 512 B, respectively, and
the first number is not limited to 8.
The I/O controller 1352 reads data from the high-speed storage
device 11 or the low-speed storage device 12 in accordance with an
access request for a data read from the host 20. Similarly, the I/O
controller 1352 writes data to the high-speed storage device 11 or
the low-speed storage device 12 in accordance with an access
request for a data write from the host 20.
The I/O management unit 1353 manages I/O (access) corresponding to
the access request from the host 20. Mainly for this I/O
management, the I/O management unit 1353 divides the storage area
of the logical unit into the above-mentioned plurality of logical
extents. That is, the I/O management unit 1353 manages the storage
area of the logical unit as a storage area including the plurality
of logical extents. The I/O management includes allocating the
physical blocks in the storage areas of the high-speed storage
device 11 and the low-speed storage device 12 to the logical blocks
in the storage area of the logical unit, and managing the state of
allocation. The address translation table 1331 is used to manage
the state of allocation. The dividing operation into the logical
extents may be executed by the configuration management unit 1351.
The I/O management also includes acquiring an access (I/O)
statistical value (hereinafter, referred to as an access count)
indicating the status of access to each logical extent. Access
counts associated with respective logical extents are managed using
the extent management table 1332.
The group management unit 1354 manages the strength of linkage of a
respective combination of two different logical extents included in
the plurality of logical extents, based on the degree of linkage of
the respective combination that indicates a degree at which the two
logical extents are sequentially accessed. The degree of linkage of
each combination is managed using the link management table 1333.
The group management unit 1354 further manages, as an extent group,
a set of logical extents included in each series of combinations
that mutually have a linkage relationship.
The tiering controller 1355 transfers (rearranges), to a physical
extent in the high-speed storage device 11, data in a physical
extent that is included in the low-speed storage device 12 and has
a high frequency of access. Similarly, the tiering controller 1355
transfers, to a physical extent in the low-speed storage device 12,
data in a physical extent that is included in the high-speed
storage device 11 and has a low frequency of access.
FIG. 3 shows an exemplary relationship between the physical extents
and the physical blocks in the embodiment. As shown in FIG. 3, the
storage area of the high-speed storage device 11 is divided into m
physical extents PE0, PE1, . . . , PEm-1. That is, the high-speed
storage device 11 includes m physical extents PE0 to PEm-1. The
storage area of the high-speed storage device 11 is further divided
into m.times.n physical blocks PB0_0, . . . , PB0_n-1, PB1_0, . . .
, PB1_n-1, . . . , PBm-1_0, . . . , PBm-1_n-1. That is, the
high-speed storage device 11 includes m.times.n physical blocks
PB0_0, . . . , PB0_n-1, PB1_0, . . . , PB1_n-1, . . . , PBm-1_0, .
. . , PBm-1_n-1.
An i-th (i=0, 1, . . . , m-1) physical extent in the high-speed
storage device 11 will hereinafter be referred to as physical
extent PEi. Physical extent PEi includes n physical blocks PBi_0 to
PBi_n-1 that are sequentially arranged in the storage area of the
high-speed storage device 11. In other words, physical blocks PBi_0
to PBi_n-1 constitute the physical extent PEi. The sign "n"
represents the above-mentioned first number, and is 8 in the
embodiment where the extent size is 4 KB and the block size is 512
B.
The above-described relationship between the physical extents and
the physical blocks in the high-speed storage device 11 is also
applicable to the low-speed storage device 12. In a similar
description associated with the low-speed storage device 12, it is
sufficient if the above description is rewritten to change the
high-speed storage device 11 to the low-speed storage device 12,
and to change the sign "m" to another sign (for example, "d"). The
sign "d" represents the number of physical extents in the low-speed
storage device 12.
Physical extent PEi in the high-speed storage device 11 is denoted
by, for example, physical extent number 0i. That is, physical
extent number 0i is an identifier for identifying physical extent
PEi. Physical extent number 0i is obtained by coupling, for
example, storage number 0 to internal physical extent number i.
Storage number 0 is used as an identifier (storage identifier) for
identifying the high-speed storage device 11. Internal physical
extent number i is used as an identifier (extent identifier) for
identifying the i-th physical extent (namely, physical extent PEi)
in a storage device denoted by storage number 0 (namely, the
high-speed storage device 11).
J-th physical block PBi_j (j=0, 1, . . . , n-1) in physical extent
PEi is denoted by physical extent number 0i and offset OFSTj.
Offset OFSTj represents the relative position of a j-th physical
block (namely, physical block PBi_j) in physical extent PEi.
Similarly, k-th physical extent PEk (k=0, 1, . . . , h-1) in the
low-speed storage device 12 is denoted by physical extent number
1k. Physical extent number 1k is obtained by coupling storage
number 1 and internal physical extent number k. Storage number 1 is
used as an identifier that denotes the low-speed storage device 12.
Internal physics extent number k is used as an identifier for
identifying a k-th physical extent (namely, physical extent PEk) in
a storage device denoted by storage number 1 (namely, the low-speed
storage device 12).
J-th physical block PBk_j in physical extent PEk is denoted by
physical extent number 1k and offset OFSTj. Above-mentioned
physical extent numbers 0i and 1k are unique in the entire physical
storage area (physical address space) provided using the high-speed
storage device 11 and the low-speed storage device 12.
FIG. 4 shows an exemplary relationship between the logical extents
and the logical blocks in the embodiment. FIG. 4 shows a logical
unit LU. The storage area (more specifically, the virtual storage
area) of the logical unit LU is divided into u.times.n logical
blocks LB0_0, . . . , LB0_n-1, LB1_0, . . . , LB1_n-1, . . . ,
LBu-1_0, . . . , LBu-1_n-1. That is, the logical unit LU includes
u.times.n logical blocks LB0_0, . . . , LB0_n-1, LB1_0, . . . ,
LB1_n-1, . . . , LBu-1_0, . . . , LBu-1_n-1. Further, the storage
area of the logical unit LU is divided into u logical extents LE0,
. . . , LEu-1. That is, the logical unit LU includes u logical
extents LE0 to LEu-1.
Assume here that the s-th logical extent (s=0, 1, . . . , u-1) in
the logical unit LU is expressed as logical extent LEs. Logical
extent LEs includes n logical blocks LBs_0 to LBs_n-1 continuously
arranged in the storage area of the logical unit LU. In other
words, logical blocks LBs_0 to LBs_n-1 constitute logical extent
LEs. Logical blocks LBs_0 to LBs_n-1 are a (u.times.n)-th logical
block to an (s+1).times.(n-1)-th logical block in the logical unit
LU, respectively.
In the embodiment, the storage controller 13 can recognize logical
blocks LB0_0, . . . , LB0_n-1, LB1_0, . . . , LB1_n-1, . . . ,
LBu-1_0, . . . , LBu-1_n-1 in the logical unit LU, and logical
extents LE0, . . . , LEu-1 in the logical unit LU. In contrast, the
host 20 can recognize only logical blocks LB0_0, . . . , LB0_n-1,
LB1_0, . . . , LB1_n-1, . . . , LBu-1_0, . . . , LBu-1_n-1.
However, this may be modified such that the configuration
management unit 1351 notifies the host 20 of definition contents
associated with each logical extent and including a logical extent
size thereof, thereby enabling the host 20 to recognize logical
extents LE0 to LEu-1 in the logical unit LU.
The host 20 recognizes (designates) the t-th logical block (t=0, 1,
. . . , u.times.(n-1)) in the logical unit LU, based on logical
unit number LUN and logical block address LBAt (LBA=LBAt=t).
Logical unit number LUN (for example, 0) is used as an identifier
for denoting the logical unit LU, and logical block address LBAt is
used as an address for indicating the t-th logical block in a
logical unit (more specifically, logical unit LU denoted by logical
unit number LUN).
The t-th logical block (namely, a logical block with logical block
address LBAt=t) in logical unit LU is expressed as LBv_w (logical
block LBv_w) where v (v=0, 1, . . . , n-1) represents the quotient
of t/n, and w (w=0, 1, . . . , n-1) represents the residue of t/n.
LBv_w denotes a w-th logical block in a v-th logical extent in
logical unit LU. As is evident, t is equal to
v.times.n+w=(v+1).times.n-(n-w). In the embodiment, the I/O
management unit 1353 divides logical block address LBAt (=t) by n,
thereby specifying logical extent LEv to which the logical block
(LBv_w) designated by logical block address LBAt belongs, and the
relative position w of the logical block in logical extent LEv.
FIG. 5 shows a data structure example of the address translation
table 1331 shown in FIG. 2. The address translation table 1331 has
a group of entries associated with all logical blocks of all
logical units provided by, for example, the configuration
management unit 1351. Each entry of the address translation table
1331 includes a logical unit number (LUN) field, a logical block
address (LBA) field, a logical extent number (LEN) field, a
physical extent number (PEN) field, and an offset field.
The LUN field is used to hold a logical unit number that denotes a
logical unit including a corresponding logical block. The LBA field
is used to hold the address (logical block address) of the
corresponding logical block.
The LEN field is used to hold a logical extent number as an
identifier for identifying a logical extent including the
corresponding logical block. The logical extent number is unique in
the entire logical storage area (logical address space), to which
all logical units provided by the configuration management unit
1351 belong. The logical extent number includes a combination of
the logical unit number and the internal logical extent number. The
internal logical extent number is unique in the logical unit
including the corresponding logical block, and is an identifier for
identifying a logical extent that includes the corresponding
logical block of the logical unit.
The PEN field is used to hold a physical extent number. The
physical extent number denotes a physical extent allocated to the
logical extent including the corresponding logical block (namely, a
physical extent including a physical block allocated to the
corresponding logical block). The offset field is used to hold an
offset (offset data). The offset indicates the relative position of
the physical block, allocated to the corresponding logical block,
in the physical extent including the physical block.
FIG. 6 shows a data structure example of the extent management
table 1332 shown in FIG. 2. The extent management table 1332 has a
group of entries associated with all logical extents in all logical
units provided by, for example, the configuration management unit
1351. Each entry of the extent management table 1332 includes a
logical extent number (LEN) field, an extent group number (EGN)
field, a preceding link extent (PLE) field, a succeeding link
extent (SLE) field, an access count (AC) field, and a last access
time (LAT) field.
The LEN field is used to hold a logical extent number that
represents a corresponding logical extent. The EGN field is used to
hold an extent group number as an identifier for identifying an
extent group to which the corresponding logical extent belongs. In
the example of the extent management table 1332 shown in FIG. 6, a
value of 0 is set in the EGN fields of all entries. The value of 0
in the EGN field is an initial value, and indicates that the
corresponding logical extent does not belong to the extent group.
Therefore, it is assumed in the embodiment that the use of an
extent group number of 0 is inhibited. However, the initial value
of the EGN field is not limited to 0. It is sufficient if the
initial value is a particular value other than usable extent group
numbers.
The PLE field and the SLE field are used Lo hold logical extent
numbers allocated to a preceding link extent and a succeeding link
extent, respectively. The preceding link extent indicates a logical
extent accessed immediately before the corresponding logical
extent. Similarly, the succeeding link extent indicates a logical
extent accessed immediately after the corresponding logical
extent.
In the example of the extent management table 1332 shown in FIG. 6,
a value of 0 is set in the PLE fields and the SLE fields of all
entries. The value of 0 in the PLE fields and the SLE fields is an
initial value, and indicates that the corresponding logical extent
does not have any preceding or succeeding logical extent in order
of access. In view of this, it is assumed in the embodiment that
the use of the logical extent number of 0 is inhibited. However,
the initial value of the PLE field and the SLE field is not limited
to 0. It is sufficient if the initial value is a particular value
other than usable logical extent numbers.
If a particular value other than the initial value and the logical
extent number, for example, -1, is set in the PLE field, this
particular value (-1) indicates that the corresponding logical
extent has no preceding logical extent in order of access.
Similarly, if -1 is set in the SLE field, the particular value (-1)
indicates that the correcting logical extent does not have any
succeeding logical extent in order of access. Further, different
particular values (e.g., -1 and -2), which differ from the initial
value and the logical extent number, may be set in the PLE field
and the SLE field, respectively.
The AC field is used to hold an access count (access frequency)
that indicates the number of accesses to the corresponding logical
extent. The LAT field is used to hold last access time data that
indicates the time (date and time) when the corresponding logical
extent is last accessed.
Respective entries of the extent management table 1332 are
initialized as follows: First, the logical extent numbers of
logical extents associated with the respective entries are set in
the LEN fields of the respective entries. 0, for example, is set in
the other fields of the respective entries. FIG. 6 shows the
initialized extent management table 1332.
FIG. 7 shows a data structure example of the link management table
1333 shown in FIG. 2. The link management table 1333 has a matrix
data structure. That is, the link management table 1333 has a
plurality of items arranged in rows and columns. In the respective
row items, unique logical extent numbers are set. In the respective
column items, unique logical extent numbers are set. The number of
row items is identical to that of column items. Further, in the
embodiment, the order of the logical extent numbers in all rows
coincides with the order of logical extent numbers in all
columns.
In FIGS. 7, A, B, C, D, E and F represent the logical extent
numbers of respective logical extents A, B, and C, D, E and F,
respectively. Assume here that an x-th row (x=1, 2, . . . ) and a
y-th row (y=1, 2, . . . , y.noteq.x) in the matrix correspond to
extent number X (X=A, B, C, D, E, F, . . . ) and extent number Y
(Y=A, B, C, D, E, F, . . . , Y.noteq.X), respectively, and
therefore that the x-th column and the y-th column in the matrix
also correspond to extent numbers X and Y, respectively. Logical
extents represented by extent numbers X and Y will hereinafter be
referred to as logical extents X and Y, respectively.
The position (x, y) of the x-th row and the y-th column in the
matrix, namely, entry (x, y) of the x-th row and the y-th column in
the link management table 1333, is used to hold the number of
accesses to, for example, logical extent Y immediately before or
after accesses to logical extent X. Similarly, the position (y, x)
of the y-th row and the x-th column in the matrix, namely, entry
(y, x) of the y-th row and the x-th column in the link management
table 1333, is used to hold the number of accesses to, for example,
logical extent X immediately before or after accesses to logical
extent Y.
The numbers held in entries (x, y) and (y, x) are identical to each
other. These numbers indicate the number of successive accesses to
logical extents X and Y in this order or vice versa. This number
indicates the strength of association (namely, the strength of
linkage) of logical extents X and Y in successive accesses. Thus,
this number will hereinafter be referred to as a degree of linkage.
The degree of linkage in each of entries (x, y) and (y, x) is
incremented by 1 by the group management unit 1354, when logical
extent Y is accessed immediately after logical extent X, or when
logical extent X is accessed immediately after logical extent
Y.
The initial value (namely, the initial degree of linkage) in
entries (x, y) and (y, x) in the link management table 1333 is, for
example, 0. In the link management table 1333 shown in FIG. 7,
blank entries indicate entries where a linkage degree of 0 is set.
If necessary, a value of 0 may be set in the blank entries of the
link management table 1333.
In the embodiment, the link management table 1333 has a matrix
structure. However, the link management table 1333 may have an
arrangement of linkage degrees corresponding to all combinations of
logical extents that have a linkage relationship (namely, a list
structure).
Referring next to FIG. 8, a description will be given of the
operation of the embodiment, using access processing as an example.
FIG. 8 is a flowchart showing an exemplary procedure of the access
processing. Assume first that the host 20 has issued an access
request to the storage controller 13 of the tiered storage system
10 through the host interface bus 30.
The HIF controller 131 of the storage controller 13 receives, from
the host interface bus 30, the access request issued by the host
20. The access request includes logical unit number LUN, logical
block address LBAt, and data transfer size. The data transfer size
indicates the number of logical blocks to be transferred
(accessed). If the data transfer size is N, the access request
designates an access to a range of successive N logical blocks that
begins with logical block address LBAt.
The I/O management unit 1353 of the storage controller 13 specifies
a logical extent range corresponding to the logical block range
designated by the received access request, as described below (step
S1). First, the I/O management unit 1353 refers to entries in the
address translation table 1331 associated with combinations of
logical unit numbers and logical block addresses indicating
respective logical blocks in the designated logical block range.
After that, the I/O management unit 1353 determines logical extents
denoted by the logical extent numbers associated with the
respective logical blocks included in the designated logical block
range. Thus, the I/O management unit 1353 specifies the logical
extent range corresponding to the designated logical block range.
Since the specified logical extent range corresponds to the logical
block range designated by the access request from the host 20, it
can be regarded as (indirectly) designated by the access request
from the host 20.
Upon specifying of the logical extent range (step S1), the group
management unit 1354 is started. The group management unit 1354
performs, in cooperation with the I/O management unit 1353, table
update processing for updating the extent management table 1332 and
the link management table 1333 based on the specified logical
extent range (step S2).
Referring now to FIG. 9, the table update processing (step S2) will
be described in detail. FIG. 9 is a flowchart showing an exemplary
procedure of the table update processing. First, the group
management unit 1354 refers to a particular area in the memory 133
(step S21). This particular area is used to store the logical
extent number of a logical extent last processed in the access
processing shown by the flowchart of FIG. 8, as will be described
later.
Next, the group management unit 1354 determines whether a valid
logical extent number is stored in the particular area in the
memory 133 (step S22). If no valid logical extent number is stored
(No in step S22), the group management unit 1354 determines that
the current access processing is access processing performed first
after the initialization of the extent management table 1332 and
the link management table 1333. In this case, the group management
unit 1354' selects, as LE1 (logical extent LE1), a leading logical
extent in the specified logical extent range (step S23). After
that, the group management unit 1354 performs first table update
processing (step S24), thereby completing the table update
processing according to the flowchart of FIG. 9.
In contrast, if a valid logical extent number (LENz) is stored in
the particular area (Yes in step S22), the group management unit
1354 determines that access processing preceding to the current
access processing has already been executed, and that the LENz
denotes a logical extent last processed (accessed) in the preceding
access processing. In this case, the group management unit 1354
selects, as LE1, the logical extent denoted by the LENz (step S25).
Further, the group management unit 1354 selects, as LE2 (logical
extent LE2), a leading logical extent in the specified logical
extent range (step S26). After that, the group management unit 1354
performs second table update processing (step S27), thereby
completing the table update process according to the flowchart of
FIG. 9.
Referring then to FIG. 10, the first table update processing (step
S24) will be described in detail. FIG. 10 is a flowchart showing an
exemplary procedure of the first table update processing. Step S23
of FIG. 9 may be performed at the beginning of the first table
update processing.
The group management unit 1354 first determines whether a logical
extent subsequent to current logical extent LE1 (namely, the
logical extent selected in step S23 of FIG. 9) exists in the
specified logical extent range (step S31). If the specified logical
extent range includes a plurality of logical extents, the
subsequent logical extent exists (Yes in step S31). In this case,
the group management unit 1354 selects the subsequent logical
extent as LE2 (step S32). Hereinafter, the logical extent numbers
(LENs) of LE1 and LE2 will be referred to as LEN_LE1 and LEN_LE2,
respectively. Furthermore, entries in the extent management table
1332 associated with LE1 and LE2 will be referred to as EMTE_LE1
and EMTE_LE2, respectively.
Next, the group management unit 1354 changes the contents (initial
values 0) of the EGN field, the PLE field and the SLE field of
entry EMTE_LE1 to the leading EGN (=1), -1 and LEN_LE2,
respectively (step S33). At this time, an EGN other than the
leading EGN may be used. On the other hand, the I/O management unit
1353 updates the contents of the AC field and the LAT field of
entry EMTE_LE1 (step S34). That is, the I/O management unit 1353
increments, by 1, the contents (initial value 0) of the AC field,
and updates the contents (initial value 0) of the LAT field so as
to indicate a current time.
Next, the group management unit 1354 changes the contents (initial
values 0) of the EGN field, the PLE field and the SLE field of
entry EMTE_LE2, to the leading EGN (=1), LEN_LE1 and -1,
respectively (step S35). Further, the group management unit 1354
updates the contents of the AC field and the LAT field of entry
EMTE_LE2 (step S36). The group management unit 1354 increments, by
1, the contents (degree of linkage) of an entry of the link
management table 1333 associated with the combination of LE1 and
LE2 (step S37).
Next, the group management unit 1354 determines whether a
subsequent logical extent (namely, a logical extent subsequent to
current logical extent LE2) exists in the specified logical extent
range (step S38). If no subsequent logical extent exists (No in
step S38), the group management unit 1354 completes the first table
update processing (step S24 of FIG. 9) according to the flowchart
of FIG. 10. That is, the group management unit 1354 completes the
table update processing (step S2 of FIG. 8) according to the
flowchart of FIG. 9.
In contrast, if a subsequent logical extent exists (Yes in step
S38), the group management unit 1354 selects current LE2 as new LE1
(step S39). Moreover, the group management unit 1354 selects, as
new LE2, the subsequent logical extent (namely, a logical extent
subsequent to new LE1) in the specified logical extent range (step
S40).
Next, the group management unit 1354 changes, from -1 to LEN_LE2,
the contents of the SLE field of entry EMTE_LE1 associated with new
LE1 (namely, entry EMTE_LE2 associated with preceding LE2) (step
S41). After that, the group management unit 1354 returns to step
S35.
In step S31, assume that no subsequent logical extent exists. That
is, the specified logical extent range includes only a single
logical extent. In this case (No in step S31), the group management
unit 1354 changes the contents of the EGN field, the PLE field and
the SLE field of entry EMTE_LE1 to the leading EGN (=1), -1 and -1,
respectively (step S42). On the other hand, the I/O management unit
1353 updates the contents of the AC field and the LAT field of
entry EMTE_LE1, as in step S34 (step S43). This is the termination
of the first table update processing (step S24 of FIG. 9) of the
group management unit 1354 according to the flowchart of FIG.
10.
Referring next to FIG. 11, second table update processing (step S27
of FIG. 9) will be described in detail. FIG. 11 is a flowchart
showing an exemplary procedure of the second table update
processing. Steps S25 and S26 of FIG. 9 may be performed at the
beginning of the second table update processing.
First, the group management unit 1354 acquires contents LEN_SLE
(LE1) of the SLE field of entry EMTE_LE1 and contents LEN_PLE (LE2)
of the PLE field of entry EMTE_LE2 from entries EMTE_LE1 and
EMTE_LE2 associated with current LE1 and LE2 (step S51). Next, the
group management unit 1354 changes the contents of the SLE field of
entry EMTE_LE1 to LEN_LE2 (step S52).
After that, the group management unit 1354 changes the current
contents of the EGN field and the SLE field of entry EMTE_LE2 in
accordance with the contents of the EGN field and the SLE field of
entry EMTE_LE2 (step S53). Step S53 will now be described in
detail.
In step S53, the group management unit 1354 determines whether the
contents of the EGN field of entry EMTE_LE2 differs from EGN_LE1
(=EGN.alpha.) indicating extent group (EG.alpha.) to which LE1
belongs. If so, the group management unit 1354 changes the contents
of the EGN field to EGN.alpha.. Further, in step S53, if the
contents of the SLE field of entry EMTE_LE2 is the initial value of
0, the group management unit 1354 changes the contents of the SLE
field to -1.
Assume here that the contents of the EGN field of entry EMTE_LE2
differs from EGN.alpha., and also differs from the initial value of
0. That is, assume that LE2 belongs to extent group EG.beta.
different from EG.alpha.. In this case, the group management unit
1354 changes the contents of the SLE field of entry EMTE_LE2 to -1,
even if the contents of the SLE field assumes a value other than
the initial value of 0 (and -1), that is, even if it is the logical
extent number of logical extent LE.gamma. belonging to EG.beta.. In
order to cancel the linkage of LE2 and LE.gamma., the group
management unit 1354 changes, to the initial value of 0, the
contents of an entry of the link management table 1333 associated
with the combination of LE2 and LE.gamma..
After executing step S53, the group management unit 1354 proceeds
to step S54. In step S54, the group management unit 1354 changes
the contents of the PLE field of entry EMTE_LE2 to LEN_LE1. On the
other hand, the I/O management unit 1353 updates the contents of
the AC field and the LAT field of entry EMTE_LE2, as in step S34
(step S55).
At this time, the group management unit 1354 increments, by 1, the
degree of linkage corresponding to the combination of LE1 and LE2
(step S56). Next, the group management unit 1354 determines whether
acquired LEN_SLE (LE1) differs from LEN_LE2, and is other than -1
(more specifically, other than -1 and 0) (step S57). Hereinafter, a
logical extent denoted by LEN_SLE (LE1) will be referred to as
LEs.
If the answer in step S57 is Yes, the group management unit 1354
determines that it is necessary to cancel the linkage of LEs and
LE1, in order to link LE2 to LE1. Therefore, the group management
unit 1354 delinks LEs from LE1 (step S58). That is, the group
management unit 1354 changes (sets), to 0, the degree of linkage
corresponding to the combination of LEs and LE1, and changes, to
-1, the contents of the PLE field of entry EMTE_LEs. After that,
the group management unit 1354 proceeds to step S59. In contrast,
if the answer in step S57 is No, the group management unit 1354
skips step S58 and proceeds to step S59.
In step S59, the group management unit 1354 determines whether
acquired LEN_PLE (LE2) differs from LEN_LE1, and is other than -1
(more specifically, other than -1 and 0). Hereinafter, a logical
extent denoted by LEN_PLE (LE2) will be referred to as LEp.
If the answer in step S59 is Yes, the group management unit 1354
determines that it is necessary to cancel the linkage of LEp and
LE1, in order to link LE2 to LE1. Therefore, the group management
unit 1354 delinks LEp from LE1 (step S60). That is, the group
management unit 1354 changes, to 0, the degree of linkage
corresponding to the combination of LEp and LE1, and changes, to
-1, the contents of the SLE field of entry EMTE_LEp.
Next, the group management unit 1354 determines whether LEN_SLE
(LE1) is equal to LEN_PLE (LE2) (step S61). In the flowchart of
FIG. 11, step S61 is executed regardless of the determination
result of step S57, if the answer in step S59 is Yes. However, step
S60 may be executed if the answers in steps S57 and S59 are both
Yes.
If LEN_SLE (LE1) is equal to LEN_PLE (LE2) (Yes in step S61), the
group management unit 1354 determines that LEs and LEp denote the
same logical extent, and LEs (=LEp) is to be delinked from the
extent group to which LE1 and LE2 belong. In this case, the group
management unit 1354 changes the contents of the EGN field of entry
EMTE_LEs (=LEp) to an EGN that denotes a new extent group (step
S62).
Next, the group management unit 1354 determines whether a
subsequent logical extent (namely, a logical extent subsequent to
current logical extent LE2) exists in the specified logical extent
range (step S63). If no subsequent logical extent exists (No in
step S63), the group management unit 1354 completes the second
table update processing (step S27 of FIG. 9) according to the
flowchart of FIG. 11. That is, the group management unit 1354
completes the table update processing (step S2 of FIG. 8) according
to the flowchart of FIG. 9.
In contrast, if the subsequent logical extent exists (Yes in step
S63), the group management unit 1354 selects current LE2 as new LE1
(step S64). Moreover, the group management unit 1354 selects, as
new LE2, a subsequent logical extent in the specified logical
extent range (step S65). After that, the group management unit 1354
returns to step S51.
Referring then to FIGS. 12 and 13, in addition to FIGS. 6 and 7, a
description will be given of a specific example of the
above-described table update processing, using a first case as an
example. The first case is that where table update processing (step
S2 of FIG. 8) is performed in accordance with a first access
request from the host 20. In this case, assume that the extent
management table 1332 and the link management table 1333 are set in
the initial states shown in FIGS. 6 and 7, respectively. FIGS. 12
and 13 show examples of the extent management table 1332 and the
link management table 1333 obtained after table update processing
is executed in response to the first access request.
First, assume that a logical extent range, which is specified based
on the first access request, covers two logical extents A and B,
and logical extent B succeeds logical extent A. In this case, the
group management unit 1354 selects logical extent A as LE1 (step
S23 of FIG. 9). After that, the group management unit 1354
performs, in cooperation with the I/O management unit 1353, the
first table update processing (step S24 of FIG. 9) in accordance
with the flowchart of FIG. 10, as described below.
First, the group management unit 1354 selects, as LE2, logical
extent B succeeding logical extent A (steps S31 and S32). Next, the
group management unit 1354 changes the contents of the EGN field,
the PLE field and the SLE field of entry EMTE_A associated with
logical extent A (=LE1) from 0, 0 and 0 shown in FIG. 6 to 1
(leading EGN), -1 and B shown in FIG. 12, respectively (step S33).
The leading EGN is determined by the group management unit 1354. On
the other hand, the I/O management unit 1353 increments, by 1, the
contents of the AC count field of entry EMTE_A from 0 shown in FIG.
6 to 1 shown in FIG. 12, and updates the contents of the LAT field
of entry EMTE_A to indicate the current time (step S34).
Subsequently, the group management unit 1354 changes the contents
of the EGN field, the PLE field and the SLE field of entry EMTE_B
associated with logical extent B (=LE2) from 0, 0 and 0 shown in
FIG. 6 to 1 (leading EGN), A and -1 shown in FIG. 12, respectively
(step S35). On the other hand, the I/O management unit 1353
increments, by 1, the contents of the AC count field of entry
EMTE_B from 0 shown in FIG. 6 to 1 shown in FIG. 12, and updates
the contents of the LAT field of entry EMTE_B to indicate the
current time (step S36).
Then, the group management unit 1354 increments, by 1, the degree
of linkage in entries (A, B) and (B, A) of the linkage management
table 1333 associated with logical extents A and B, from 0
(indicated by the blank space) shown in FIG. 7 to 1 shown in FIG.
13 (step S37). The group management unit 1354 stores, as valid
logical extent number LENz in the particular area of the memory
133, logical extent number B of logical extent B (namely, last
logical extent B in the logical extent range specified based on the
first access request) last processed in the above-described access
processing including the table update processing (step S18 of FIG.
8).
Referring next to FIGS. 14 and 15, in addition to FIGS. 12 and 13,
a specific example of the above-described table update processing
will be described using a second case as an example. The second
case is that where table update processing (step S2 of FIG. 8) is
performed in accordance with a second access request issued from
the host 20 after the first access request. At this time, the
extent management table 1332 and the link management table 1333
assume the states shown in FIGS. 12 and 13, respectively. FIGS. 14
and 15 show examples of the extent management table 1332 and the
link management table 1333 obtained after table update processing
is executed in response to the second access request.
Assume here that a logical extent range, which is specified from
the second access request, covers two logical extents C and D, and
logical extent D succeeds logical extent C. At this time, logical
extent number B of logical extent B is stored in the particular
area of the memory 133. Logical extent B is the last logical extent
in the logical extent range specified based on the first access
request. As is evident, logical extent B precedes logical extent C
in order of access, and logical extent C succeeds logical extent B
in order of access. That is, logical extents B and C are successive
in order of access.
In this case, the group management unit 1354 selects logical
extents B and C as LE1 and LE2, respectively (steps S25 and S26 of
FIG. 9). Then, the group management unit 1354 performs, in
cooperation with the I/O management unit 1353, the second table
update processing (step S27 of FIG. 9) in accordance with the
flowchart of FIG. 11, as described below.
The group management unit 1354 changes the contents of the SLE
field of entry EMTE_B of the extent management table 1332
associated with logical extent B (=LE1), from -1 shown in FIG. 12
to C shown in FIG. 14 (step S52). The group management unit 1354
also changes the contents of the EGN field and the SLE field of
entry EMTE_C of the extent management table 1332 associated with
logical extent C (=LE2), from 0 and 0 shown in FIG. 12 to 1
(namely, the EGN of an extent group including preceding logical
extent B) and -1 shown in FIG. 14, respectively (step S53).
The group management unit 1354 further changes the contents of the
PLE field of entry EMTE_C from 0 shown in FIG. 12 to B shown in
FIG. 14 (step S54). On the other hand, the I/O management unit 1353
increments, by 1, the contents of the AC count field of entry
EMTE_C from 0 shown in FIG. 12 to 1 shown in FIG. 14, and updates
the contents of the LAT field of entry EMTE_C to indicate the
current time (step S55). Then, the group management unit 1354
increments, by 1, the degree of linkage in entries (B, C) and (C,
B) of the linkage management table 1333 associated with logical
extents B and C, from 0 (indicated by the blank space) shown in
FIG. 13 to 1 shown in FIG. 15 (step S56).
Then, the group management unit 1354 selects logical extents C and
D as LE1 and LE2, respectively (steps S64 and S65 of FIG. 11).
Further, the group management unit 1354 changes the contents of the
SLE field of entry EMTE_C from -1 to D as shown in FIG. 14 (step
S52). The group management unit 1354 also changes the contents of
the EGN field and the SLE field of entry EMTE_D of the extent
management table 1332 associated with logical extent D, from 0 and
0 shown in FIG. 12 to 1 (namely, the EGN of the extent group
including preceding logical extent C) and -1 shown in FIG. 14,
respectively (step S53).
The group management unit 1354 further changes the contents of the
PLE field of entry EMTE_D from 0 shown in FIG. 12 to C shown in
FIG. 14 (step S54). On the other hand, the I/O management unit 1353
increments, by 1, the contents of the AC count field of entry
EMTE_D from 0 shown in FIG. 12 to 1 shown in FIG. 14, and updates
the contents of the LAT field of entry EMTE_D to indicate the
current time (step S55).
Subsequently, the group management unit 1354 increments, by 1, the
degree of linkage in entries (C, D) and (D, C) of the linkage
management table 1333 associated with logical extents C and D, from
0 (indicated by the blank space) shown in FIG. 13 to 1 shown in
FIG. 15 (step S56). The group management unit 1354 stores, in the
particular area of the memory 133, logical extent number D of
logical extent D last processed in the above-described access
processing including the table update processing (step S18 of FIG.
8).
Referring next to FIGS. 16 and 17, in addition to FIGS. 14 and 15,
a description will be given of a specific example of the
above-described table update processing, using a third case as an
example. The third case is that where table update processing (step
S2 of FIG. 8) is performed in accordance with a third access
request issued from the host 20 after the second access request. At
this time, the extent management table 1332 and the link management
table 1333 assume the states shown in FIGS. 14 and 15,
respectively. FIGS. 16 and 17 show examples of the extent
management table 1332 and the link management table 1333 obtained
after table update processing is executed in response to the third
access request.
Assume here that a logical extent range, which is specified based
on the third access request, covers two logical extents A and B. At
this time, logical extent number D of logical extent D is stored in
the particular area of the memory 133. Logical extent D is the last
logical extent in the logical extent range specified based on the
second access request. As is evident, logical extents D and A are
successive in order of access.
In this case, the group management unit 1354 selects logical
extents D and A as LE1 and LE2, respectively (steps S25 and S26 of
FIG. 9). Subsequently, the group management unit 1354 performs, in
cooperation with the I/O management unit 1353, the second table
update processing (step S27 of FIG. 9) in accordance with the
flowchart of FIG. 11, as described below.
The group management unit 1354 changes the contents of the SLE
field of entry EMTE_D of the extent management table 1332
associated with logical extent D (=LE1), from -1 shown in FIG. 14
to A shown in FIG. 16 (step S52). At this time, the group
management unit 1354 changes neither of the contents (1 and B) of
the EGN field and the SLE field of entry EMTE_A of the extent
management table 1332, associated with logical extent A (=LE2)
(step S53).
The group management unit 1354 also changes the contents of the PLE
field of entry EMTE_A from -1 shown in FIG. 14 to D shown in FIG.
16 (step S54). On the other hand, the I/O management unit 1353
increments, by 1, the contents of the AC count field of entry
EMTE_A from 1 shown in FIG. 14 to 2 shown in FIG. 16, and updates
the contents of the LAT field of entry EMTE_A to indicate the
current time (step S55). After that, the group management unit 1354
increments, by 1, the degree of linkage in entries (D, A) and (A,
D) of the linkage management table 1333 associated with logical
extents D and A, from 0 (indicated by the blank space) shown in
FIG. 15 to 1 shown in FIG. 17 (step S56).
After that, the group management unit 1354 selects logical extents
A and B as LE1 and LE2, respectively (steps S64 and S65). Next, the
group management unit 1354 acquires contents LEN_SLE (A) of the SLE
field of entry EMTE_A and contents LEN_PLE (B) of the PLE field of
entry EMTE_B from entries EMTE_A and EMTE_B associated with logical
extent A (=LE1) and logical extent B (=LE2), respectively (step
S51). Acquired LEN_SLE (A) and LEN_PLE (B) are B and A,
respectively, as is shown in FIG. 14. That is, logical extents B
and A have already been registered as the succeeding link extent of
logical extent A and the preceding link extent of logical extent B
in the extent management table 1332, respectively. This means that
logical extents A and B have already been linked to each other.
In such a case, the group management unit 1354 skips steps S52 and
S54, although this process is omitted from the flowchart of FIG.
11. As a result, as is shown in FIG. 16, the group management unit
1354 maintains contents LEN_SLE (A) and LEN_PLE (B) of the SLE
field of entry EMTE_A and the PLE field of entry EMTE_B in the
current states (namely, B and A shown in FIG. 14). At this time,
the group management unit 1354 changes neither of the contents (1
and C) of the EGN field and the SLE field of entry EMTE_B (step
S53).
Steps S52 and S54 may be executed, because B is reset in the SLE
field of entry EMTE_A by the execution of step S52, and A is reset
in the PLE field of entry EMTE_B by the execution of step S54. That
is, even if steps S52 and S54 are executed, the contents of the SLE
field of entry EMTE_A and the PLE field of entry EMTE_B is
maintained at B and A, respectively.
On the other hand, the I/O management unit 1353 increments, by 1,
the contents of the AC count field of entry EMTE_B from 1 shown in
FIG. 14 to 2 shown in FIG. 16, and updates the contents of the LAT
field of entry EMTE_B to indicate the current time (step S55).
Subsequently, the group management unit 1354 increments, by 1, the
degree of linkage in entries (A, B) and (B, A) of the linkage
management table 1333 associated with logical extents A and B, from
1 shown in FIG. 15 to 2 shown in FIG. 17 (step S56). The group
management unit 1354 stores, in the particular area of the memory
133, logical extent number B of logical extent B last processed in
the above-described access processing including the table update
processing (step S18 of FIG. 8).
Referring next to FIGS. 18 and 19, in addition to FIGS. 16 and 17,
a description will be given of a specific example of the
above-described table update processing, using a fourth case as an
example. The fourth case is that where table update processing
(step S2 of FIG. 8) is performed in accordance with a fourth access
request issued from the host 20 after the third access request. At
this time, the extent management table 1332 and the link management
table 1333 assume the states shown in FIGS. 16 and 17,
respectively. FIGS. 18 and 19 show examples of the extent
management table 1332 and the link management table 1333 obtained
after table update processing is executed in response to the fourth
access request.
Assume here that a logical extent range, which is specified based
on the fourth access request, covers two logical extents D and E.
At this time, logical extent number B of logical extent B is stored
in the particular area of the memory 133. Logical extent B is the
last logical extent in the logical extent range specified based on
the third access request. As is evident, logical extents B and D
are successive in order of access.
In this case, the group management unit 1354 selects logical
extents B and D as LE1 and LE2, respectively (steps S25 and S26 of
FIG. 9). Subsequently, the group management unit 1354 performs, in
cooperation with the I/O management unit 1353, the second table
update processing (step S27 of FIG. 9) in accordance with the
flowchart of FIG. 11, as described below.
First, the group management unit 1354 acquires contents LEN_SLE (B)
of the SLE field of entry EMTE_B and contents LEN_PLE (D) of the
PLE field of entry EMTE_D from entries EMTE_B and EMTE_D associated
with logical extents B (=LE1) and D (=LE2) (step S51). Acquired
LEN_SLE (B) and LEN_PLE (D) are both C. That is, logical extent C
has already been registered as the succeeding link extent of
logical extent B and as the preceding link extent of logical extent
D in the extent management table 1332. This means that logical
extents B and C have already been linked to each other, and logical
extents C and D have also already been linked to each other.
Next, the group management unit 1354 changes the contents of the
SLE field of entry EMTE_B of the extent management table 1332
associated with logical extent B, from C shown in FIG. 16 to D
shown in FIG. 18 (step S52). At this time, the group management
unit 1354 changes neither of the contents (1 and A) of the EGN
field and the SLE field of entry EMTE_D of the extent management
table 1332, associated with logical extent D (step S53).
The group management unit 1354 further changes the contents of the
PLE field of entry EMTE_D from C shown in FIG. 16 to B shown in
FIG. 18 (step S54). On the other hand, the I/O management unit 1353
increments, by 1, the contents of the AC count field of entry
EMTE_D from 1 shown in FIG. 16 to 2 shown in FIG. 18, and updates
the contents of the LAT field of entry EMTE_D to indicate the
current time (step S55). Then, the group management unit 1354
increments, by 1, the degree of linkage in entries (B, D) and (D,
B) of the linkage management table 1333 associated with logical
extents B and D, from 0 (indicated by the blank space) shown in
FIG. 17 to 1 shown in FIG. 19 (step S56).
Next, the group management unit 1354 determines whether acquired
LEN_SLE (B) differs from LEN_D (=D), and whether it is other than
-1 (step S57). In this example, acquired LEN_SLE (B) is C, which
differs from LEN_D (=D) and is other than -1 (Yes in step S57).
In this case, the group management unit 1354 determines that it is
necessary to cancel the linkage of logical extent C indicated by
LEN_SLE (B) and logical extent B in order to link logical extent D
to logical extent B. Therefore, the group management unit 1354
delinks logical extent C (=LEs) from logical extent B (=LE1) (step
S58). That is, the group management unit 1354 changes the degree of
linkage corresponding to the combination of logical extents C and B
from 1 shown in FIG. 17 to 0 shown in FIG. 19, and changes the
contents of the PLE field of entry EMTE_C from B shown in FIG. 16
to -1 shown in FIG. 18.
Next, determines whether acquired LEN_PLE (D) differs from LEN_B
(=B), and whether it is other than -1 (step S59). In this example,
acquired LEN_PLE (D) is C, which differs from LEN_B (=B) and is
other than -1 (Yes in step S59).
In this case, the group management unit 1354 determines that it is
necessary to cancel the linkage of logical extent C indicated by
LEN_PLE (D) and logical extent D, in order to link logical extent D
to logical extent B. Therefore, the group management unit 1354
delinks logical extent C (=LEp) from logical extent D (=LE2) (step
S60). That is, the group management unit 1354 changes the degree of
linkage corresponding to the combination of logical extents C and D
from 1 shown in FIG. 17 to 0 shown in FIG. 19, and changes the
contents of the SLE field of entry EMTE_C from D shown in FIG. 16
to -1 shown in FIG. 18.
Next, the group management unit 1354 determines whether acquired
LEN_SLE (B) and LEN_PLE (D) are equal to each other (step S61). In
this example, acquired LEN_SLE (B) and LEN_PLE (D) are both C, and
are therefore equal (Yes in step S61). This means that the logical
extent (LEs) delinked from logical extent B (=E1) in step S58 is
logical extent C that is equal to the logical extent (LEp) delinked
from logical extent D (=LE2) in step S60. Therefore, in order to
delink logical extent C from the extent group including logical
extents B and D, the group management unit 1354 changes the
contents of the EGN field of entry EMTE_C from 1 shown in FIG. 16
to an EGN (for example, 2 shown in FIG. 18) that indicates a new
extent group (step S62).
After that, the group management unit 1354 selects logical extents
D and E as LE1 and LE2, respectively (steps S64 and S65).
Subsequently, the group management unit 1354 acquires contents
LEN_SLE (D) of the SLE field of entry EMTE_D and contents LEN_PLE
(E) of the PLE field of entry EMTE_D from entries EMTE_D and EMTE_E
associated with logical extent D (=LE1) and logical extent E
(=LE2), respectively (step S51). Acquired LEN_SLE (D) and LEN_PLE
(E) are A and 0, respectively, as is shown in FIG. 16.
Next, the group management unit 1354 changes the contents of the
SLE field of entry EMTE_D from A shown in FIG. 16 to E shown in
FIG. 18 (step S52). The group management unit 1354 also changes the
contents of the EGN field and the SLE field of entry EMTE_E from 0
and 0 shown in FIG. 16 to 1 and -1 shown in FIG. 18, respectively
(step S53).
The group management unit 1354 further changes the contents of the
PLE field of entry EMTE_E from 0 shown in FIG. 16 to D shown in
FIG. 18 (step S54). On the other hand, the I/O management unit 1353
increments, by 1, the contents of the AC count field of entry
EMTE_E from 0 shown in FIG. 16 to 1 shown in FIG. 18, and updates
the contents of the LAT field of entry EMTE_E to indicate the
current time (step S55). The group management unit 1354 also
increments, by 1, the degree of linkage in entries (D, E) and (E,
D) of the linkage management table 1333 associated with logical
extents D and E, from 0 (indicated by the blank space) shown in
FIG. 17 to 1 shown in FIG. 19 (step S56).
As described above, acquired LEN_SLE (D) is A, which differs from
LEN_E (=E) and is other than -1 (Yes in step S57). In this case,
the group management unit 1354 determines that it is necessary to
cancel the linkage of logical extent A indicated by LEN_SLE (D) and
logical extent D, in order to link logical extent E to logical
extent D. Therefore, the group management unit 1354 delinks logical
extent A (=LEs) from logical extent D (=LE1) (step S58). That is,
the group management unit 1354 changes the degree of linkage
corresponding to the combination of logical extents A and D from 1
shown in FIG. 17 to 0 shown in FIG. 19, and changes the contents of
the PLE field of entry EMTE_A from D shown in FIG. 16 to -1 shown
in FIG. 18. In the embodiment, current LE2, namely, logical extent
E, is the last logical extent in the specified logical extent range
(No in step S63). Therefore, the group management unit 1354
completes the second table update processing (step S27 in FIG. 9).
That is, the group management unit 1354 completes the table update
processing (step S2 in FIG. 8).
Return to the flowchart of FIG. 8. Upon the execution of the table
update processing (step S2), the I/O controller 1352 is started.
First, the I/O controller 1352 sets, as variable e, the number of
logical extents in the specified logical extent range, in order to
execute an access requested by the received access request (step
S3). Variable e represents the number of logical extents to be
accessed (namely, logical extents access to which is
incomplete).
Next, the I/O controller 1352 selects one logical extent (namely, a
target logical extent), to be subsequently accessed, from logical
extents, the number of which is indicated by variable e (step S4).
Next, the I/O controller 1352 accesses, as described below,
physical blocks allocated to respective ones of all logical blocks
which are included in the target logical extent and to be accessed
(step S5). Assume here that the number of logical blocks to be
accessed in the target logical extent is c. In this case, the
number of physical blocks allocated to the c logical blocks is also
c.
First, the I/O controller 1352 acquires a combination of the
physical extent number and the offset of a physical block (that is,
a leading physical block) allocated to a leading logical block
included in all logical blocks to be accessed in the target logical
extent. The I/O controller 1352 acquires the combination of the
physical extent number and the offset by referring to the address
translation table 1331, based on the logical block address and the
logical extent number of the leading logical block.
By acquiring the combination of the physical extent number and the
offset of the leading physical block, the I/O controller 1352
specifies c physical blocks that are to be actually accessed and
begins with the leading physical block, and also specifies a
storage device (tier) that includes the c physical blocks. After
that, the I/O controller 1352 accesses the specified c physical
blocks in the specified storage device through the SIF controller
132. If the access request is a write access request, and if no
physical block is allocated to logical blocks falling in a logical
block range designated by the access request, the I/O management
unit 1353 allocates, during, for example, the execution of step S3,
free physical blocks continuously arranged in the high-speed
storage device 11 (upper tier), to the respective logical blocks in
the logical block range.
After accessing the specified c physical blocks (step S5), the I/O
controller 1352 returns a response to the host 20 through the HIF
controller 131 (step S6). Subsequently, the I/O controller 1352
transfers control to the tiering controller 1355. At this time, the
tiering controller 1355 determines whether the access has been made
to the low-speed storage device 12 (lower tier) (step S7).
If it has been the access to the lower tier (Yes in step S7), it is
highly likely that the target logical extent will be accessed in
near future, and hence the tiering controller 1355 determines that
the data of the physical extent allocated to the target logical
extent is to be transferred to the upper tier for the improvement
of access performance. Further, if the target logical extent
belongs to an extent group, the tiering controller 1355 determines
that the data of physical extents allocated to all the other
logical extents in the extent group also is to be transferred to
the upper tier, since it is also highly likely that the other
logical extents will be accessed in near future. In view of this,
the tiering controller 1355 executes data transfer source
determination processing for determining, as sources from which
data is to be transferred (hereinafter, referred to as data
transfer sources), one or more physical extents including the
physical extent allocated to the target logical extent (step
S8).
Referring then to FIG. 20, the data transfer source determination
processing (step S8) will be described in detail. FIG. 20 is a
flowchart showing an exemplary procedure of the data transfer
source determination processing. First, the tiering controller 1355
refers to the EGN field of an entry of the extent management table
1332 associated with the target logical extent (step S71).
Next, the tiering controller 1355 determines whether the target
logical extent belongs to the extent group, based on whether a
numerical value other than the initial value of 0 is set in the
referred EGN field (step S72). If the target logical extent belongs
to the extent group (Yes in step S72), the tiering controller 1355
proceeds to step S73. In step S73, the tiering controller 1355
specifies a set of physical extents allocated to all logical
extents in the extent group that includes the target logical
extent. Further, in step S73, the tiering controller 1355
determines, as data transfer sources, all physical extents in the
lower tier, which are included in the specified set of physical
extents. The determined data transfer sources include the physical
extent to which the target logical extent is allocated. Then, the
tiering controller 1355 completes the data transfer source
determination processing.
In contrast, if the target logical extent does not belong to the
extent group (No in step S72), the tiering controller 1355
determines, as a data transfer source, only the physical extent
allocated to the target logical extent (step S74). Then, the
tiering controller 1355 thereby completing the data transfer source
determination processing.
Returning to FIG. 8, the access processing will further be
described. After executing the data transfer source determination
processing (step S8) in accordance with the flowchart of FIG. 20,
the tiering controller 1355 proceeds to step S9. In step S9, the
tiering controller 1355 sets, as variable q, the number of physical
extents determined as the data transfer sources (step S9).
Next, the tiering controller 1355 searches the upper tier for a
free area (step S10). That is, the tiering controller 1355
searches, based on the address translation table 1331, for physical
extents (namely, free physical extents) that are included in the
upper tier (high-speed storage device 11), and are not allocated to
logical extents. If a free physical extent list is stored in the
memory 133 (local HDD 134), the tiering controller 1355 may search,
from the list, for the free physical extents in the upper tier.
Assume here that the free physical extent list holds physical
extent numbers allocated to the free physical extents.
When the tiering controller 1355 has detected the free physical
extents in the upper tier, it sets the number of free physical
extents as variable f (step S11). In step S11, the tiering
controller 1355 subtracts variable f from variable q, and sets the
difference (q-f) as variable r. Next, the tiering controller 1355
determines whether variable r (=q-f) is positive (step S12).
If variable r is positive (i.e., if q>f) (Yes in step S12), the
tiering controller 1355 determines that r free physical extents are
lacking in order to transfer, to the upper tier, the data of q
physical extents determined as data transfer sources. In this case,
the tiering controller 1355 executes free-area securing processing
for securing at least r new free physical extents in the upper tier
(step S13). After that, the tiering controller 1355 proceeds to
step S14.
In contrast, if variable r is not positive (i.e., if q.ltoreq.f)
(No in step S12), the tiering controller 1355 determines that free
physical extents sufficient to transfer the data of the q physical
extents determined as the data transfer sources already exist. In
this case, the tiering controller 1355 skips step S13, and proceeds
to step S14.
Referring to FIG. 21, the free-area securing processing (step S13)
will be described in detail. FIG. 21 is a flowchart showing an
exemplary procedure of the free-area securing processing. In the
following description, if physical extents in the upper tier are
allocated to logical extents, these logical extents will be
referred to as logical extents corresponding to the upper tier.
Similarly, if physical extents in the upper tier are allocated to
logical extents in an extent group, the extent group will be
referred to as an extent group corresponding to the upper tier.
In the free-area securing processing, first, the tiering controller
1355 generates a list associated with all logical extents
corresponding to the upper tier and not belonging to extent groups,
and associated with all extent groups corresponding to the upper
tier (step S81). The generated list includes elements associated
with the logical extents not belonging to the extent groups, and
elements associated with the extent groups.
Each of the elements in the list, which are associated with the
logical extents not belonging to the extent groups, includes a
combination of the logical extent number, the access count and the
last access time of a corresponding logical extent. Similarly, each
of the elements in the list, which are associated with the extent
groups, includes a combination of the extent group number, the
access count and the last access time of a corresponding extent
group.
In the embodiment, the tiering controller 1355 uses, as the access
count of each extent group, the average of the access counts of all
logical extents belonging to a corresponding extent group. However,
the tiering controller 1355 may use, as the access count of each
extent group, the greatest one of the access counts of all logical
extents belonging to a corresponding extent group. Moreover, in the
embodiment, the tiering controller 1355 uses, as the last access
time data of each extent group, last access time data included in
the last access time data items of all logical extents belonging to
a corresponding extent group and indicating a most recent access
time.
During the generation of the above-mentioned list, the tiering
controller 1355 specifies logical extents not belonging to the
extent groups, and extent groups, based on the extent management
table 1332. Further, the tiering controller 1355 determines whether
the specified logical extents correspond to the upper tier, by
referring to the address translation table 1331 based on the
logical extent numbers of the specified logical extents. That is,
the tiering controller 1355 determines whether the specified
logical extents correspond to the upper tier, based on the physical
extent numbers of physical extents allocated to the specified
logical extents. Similarly, the tiering controller 1355 determines
whether the specified extent groups correspond to the upper tier,
by referring to the address translation table 1331 based on the
logical extent numbers of logical extents included in the specified
extent groups. That is, based on the physical extent numbers of
physical extents allocated to the logical extents in the specified
extent groups, the tiering controller 1355 determines whether the
logical extents in the specified extent groups correspond to the
upper tier, and determines, based on this determination result,
whether the specified extent groups correspond to the upper
tier.
After the generation of the above-mentioned list, the tiering
controller 1355 sorts (for example, in an ascending order of access
count) all elements in the list, based on the access count (more
specifically, the access count and the last access time) of each
element (step S82). In this sorting, if a plurality of elements
having the same access count exist, the tiering controller 1355
arranges the elements such that the earlier the last access time,
the lower in rank the element. However, for simplification of the
description, it is assumed that if the rank of a certain element is
higher (lower) than that of another element, the access count of
the certain element is greater (smaller) than that of the other.
Moreover, the rank of the element having the smallest access count
is treated as lowest.
Next, the tiering controller 1355 sets the number of elements in
the generated list as the initial value of variable x (step S83).
Variable x is used as a pointer for indicating the position (that
is, rank) of an element (more specifically, the position (i.e.,
rank) of an element after sorting) in the generated list.
Therefore, in the description below, variable x will be referred to
as pointer x. In step S83, the tiering controller 1355 sets
variable y as an initial value of 0. Variable y represents the
number of physical extents having data transferred from the upper
tier to the lower tier in the free-area securing processing, that
is, the number of free physical extents newly secured in the upper
tier.
Next, the tiering controller 1355 determines whether an element in
the list, designated by pointer x (that is, an element of the x-th
rank), is an extent group (step S84). If the element of the x-th
rank is the extent group (Yes in step S84), the tiering controller
1355 transfers the data of physical extents, which are allocated to
the respective logical extents of the x-th rank extent group, from
the upper tier (high-speed storage device 11) to a free area in the
lower tier (low-speed storage device 12) (step S85). By this data
transfer, the tiering controller 1355 can newly secure, as free
physical extents (free area), the physical extents in the upper
tier allocated to the respective logical extents of the x-th rank
extent group.
Subsequently, the tiering controller 1355 increments variable y by
the number of physical extents whose data has been transferred by
the execution of step S84 (step S86). Thereafter, the tiering
controller 1355 proceeds to step S89.
In contrast, if the element of the x-th rank is not an extent group
(No in step S84), that is, if the element of the x-th rank is a
logical extent, the tiering controller 1355 transfers the data of a
physical extent allocated to the logical extent of the x-th rank,
from the upper tier to a free area in the lower tier (step S87). By
this data transfer, the tiering controller 1355 can secure, as a
free physical extent, a physical extent in the upper tier allocated
to the logical extent of the x-th rank. After that, the tiering
controller 1355 increments variable y by 1 (step S88), and proceeds
to step S89.
In step S89, the tiering controller 1355 updates the address
translation table 1331 to reflect data transfer in step S85 or S87.
That is, if step S89 is executed in accordance with the execution
of step S85, the tiering controller 1355 updates the address
translation table 1331 so that the physical extents (physical
blocks in the physical extents), which are allocated to the
respective logical extents (logical blocks in the logical extents)
of the x-th rank extent group, will be changed from the physical
extents (physical blocks in the physical extents) as the data
transfer sources in step S85, to physical extents (physical blocks
in the physical extents) as data transfer destinations in step S85.
In contrast, if step S89 is executed in accordance with the
execution of step S87, the tiering controller 1355 updates the
address translation table 1331 so that a physical extent allocated
to the x-th rank logical extent will be changed from the physical
extent as a data transfer source in step S87 to a physical extent
as a data transfer destination.
After updating the address translation table 1331, the tiering
controller 1355 proceeds to step S90. In step S90, the tiering
controller 1355 determines whether variable y updated at step S86
or S88 is greater than or equal to variable r. If variable y is
greater than or equal to r (Yes in step S90), the tiering
controller 1355 determines that at least r new free physical
extents have been secured in the upper tier by the free-area
securing processing. At this time, the tiering controller 1355
completes the free-area securing processing.
As described above, in the embodiment, the tiering controller 1355
does not reflect, in the extent management table 1332 or the link
management table 1333, data transfer for securing a free area,
which is performed in steps S85 and S87. However, the tiering
controller 1355 may update the extent management table 1332 and the
link management table 1333 in accordance with data transfer for
securing a free area. In this case, however, the link management
table 1333 is not updated when the data transfer is performed in
step S87.
In contrast, if variable y is less than variable r (No in step
S90), the tiering controller 1355 determines that at least r new
free physical extents have not yet secured in the upper tier. In
this case, the tiering controller 1355 continues the free-area
securing processing as follows.
First, the tiering controller 1355 decrements pointer x by 1 (step
S91). After that, the tiering controller 1355 returns to step S84,
thereby determining whether the element in the list designated by
decremented pointer x is an extent group. As is evident, the rank
of the element used in the current determination is higher by 1
than that of an element used in the last determination. Subsequent
operations are the same as those performed after the last
determination. Steps S84 to S91 are repeated until at least r new
free physical extents are secured in the upper tier.
Returning to FIG. 8, the access processing will be further
described. After executing free-area securing processing in
accordance with the flowchart of FIG. 21 (step S13), the tiering
controller 1355 proceeds to step S14. At this time, the upper tier
includes at least (f+r) (=q) physical extents. Accordingly, the
tiering controller 1355 transfers the data of the q physical
extents, determined by the data transfer source determination
processing (step S8), to the free area (more specifically, q free
physical extents) in the upper tier (step S14). The tiering
controller 1355 performs the above-described data transfer also
when the free-area securing processing (step S13) is skipped (No in
step S12) (step S14).
Next, the tiering controller 1355 updates the address translation
table 1331, the extent management table 1332 and the link
management table 1333 to reflect the data transfer in step S14
(step S15). That is, the tiering controller 1355 updates the
address translation table 1331 to allocate q physical extents
(physical blocks in the physical extents) as data transfer
destinations, to q logical extents (logical blocks in the logical
extents) to which q physical extents as data transfer sources are
allocated. The tiering controller 1355 further updates the access
counts and the last access time data items in entries of the extent
management table 1332 associated with the above-mentioned q logical
extents. Moreover, the tiering controller 1355 increments, by 1,
each of the degrees of linkage in the link management table 1333,
associated with the respective combinations of successively
accessed logical extents that are included in the above-mentioned q
logical extents.
After executing step S15, the tiering controller 1355 returns
control to the I/O controller 1352. At this time, the I/O
controller 1352 decrements variable e by 1 (step S16). After that,
the I/O controller 1352 determines whether variable e decremented
by 1 is less than zero (negative) (step S17). If variable e
decremented by 1 is less than zero (Yes in step S17), the I/O
controller 1352 determines that all logical extents in the
specified logical extent range have been accessed. Subsequently,
the I/O controller 1352 stores, in the particular area of the
memory 133, the logical extent number of the last processed target
logical extent (namely, the last logical extent in the specified
logical extent range) (step S18), thereby completing the access
processing according to the flowchart of FIG. 8.
In contrast, if variable e decremented by 1 is not less than 0 (No
in step S17), the I/O controller 1352 determines that e logical
extents that have not yet been accessed exist in the specified
logical extent range. Therefore, the I/O controller 1352 returns to
step S4, and selects, as a target logical extent, a logical extent
succeeding the preceding accessed logical extent, from e (i.e., the
number indicated by variable e) logical extents that have not yet
been accessed. After that, processing succeeding step S4 (namely,
processing including steps S5 to S7) is executed as in the case
where the target logical extent was selected in step S4 of the
first loop.
If a physical extent allocated to the target logical extent
selected at step S4 of the first loop exists in the lower tier (Yes
in step S7), data transfer from the lower tier to the upper tier is
performed at step S14 of the first loop. Because of this, if the
target logical extent selected in step S4 of the first loop belongs
to an extent group, a set of physical extents allocated to all
logical extents in the extent group exist in the upper tier after
the execution of step S14 of the first loop. Accordingly, a
physical extent allocated to a target logical extent selected in
step S4 of the second loop exists in the upper tier (No in step
S7). In this case, steps S8 to S15 are skipped, and step S16 is
executed.
Also when the physical extent allocated to the target logical
extent selected in step S4 of the first loop exists in the upper
tier (No in step S7), steps S8 to S15 are skipped, and step S16 is
executed. If the physical extent allocated to the target logical
extent selected in step S4 of the second loop exists in the lower
tier (Yes in step S7), step S8 is executed.
In the embodiment, by executing step S14 in the access processing
according to the access request, the tiering controller 1355
transfers, to the upper tier, data of all physical extents in the
lower tier included in a set of physical extents allocated to all
logical extents in an extent group, to which a logical extent range
designated in an access request from the host 20 belongs. This data
transfer can be executed with a smaller overhead within a shorter
period than a conventional data transfer between the tiers based on
periodical access frequency evaluation.
Respective logical extents in an extent group, to which a
designated logical extent range belongs, have high degrees of
linkage in simultaneous access, and may well be accessed in near
future even if they have small access counts. In the embodiment, it
is guaranteed that the data of each logical extent (i.e., the data
of a physical extent allocated thereto) in the extent group all
exists in the upper tier by the above-described data transfer.
Therefore, when an access to an arbitrary logical block range in
the above-mentioned extent group is requested in near future after
the data transfer, the I/O controller 1352 can quickly access a
physical block range corresponding to the arbitrary logical block
range.
In the flowchart of FIG. 8, the determination (step S17) associated
with variable e is performed immediately after the decrement (step
S16) of variable e. However, the determination associated with
variable e may be performed immediately before, for example, the
selection (step S4) of a target logical extent. In this case, the
I/O controller 1352 must determine whether variable e is less than
1, unlike step S17. That is, the I/O controller 1352 may proceed to
step S4 if variable e is not less than 1, and may proceed to step
S18 if variable e is less than 1. Further, the I/O controller 1352
may determine whether variable e is less than 1, after the
decrement (step S16) of variable e.
<Modification>
A modification of the embodiment will now be described. In the
embodiment, no limitations are imposed on the scale of the extent
group. Because of this, the extent group may become enormous over
time. If the extent group is enormous, a lot of time is required to
transfer, from the lower tier to the upper tier, the data of, for
example, all logical extents (i.e., the data of physical extents
allocated thereto) in the extent group. In view of this, the
modification is characterized in that an enormous extent group is
divided into two extent groups by regrouping processing.
Referring to FIG. 22, regrouping processing according to the
modification will be described. FIG. 22 is a flowchart showing the
procedure of the regrouping processing. The regrouping processing
of the modification is assumed to be added immediately before step
S3 (i.e., immediately after step S2) in the access processing shown
in the flowchart of FIG. 8. Therefore, if necessary, the regrouping
processing may be inserted between steps S2 and S3 in the flowchart
of FIG. 8.
First, the group management unit 1354 determines whether extent
group expansion has occurred, based on the result of update of the
extent management table 1332 in step S2 of FIG. 8 (step S101). The
extent group expansion means that the number of logical extents
that constitute an extent group is increased. In the
above-described second case, extent group expansion will occur.
If no extent group expansion has occurred (No in step S101), the
group management unit 1354 determines that regrouping is not
necessary. In this case, the group management unit 1354 completes
the regrouping processing according to the flowchart of FIG. 22,
and proceeds to step S3 of FIG. 8.
In contrast, if the extent group expansion has occurred (Yes in
step S101), the group management unit 1354 specifies an expanded
extent group (step S102). Next, the group management unit 1354
detects the number Ne of logical extents that constitute the
specified extent group, based on the extent management table 1332
(step S103).
To manage the number of logical extents extent group by extent
group, the group management unit 1354 may use an extent group
management table that includes entries associated with the
respective extent groups. Each entry of this extent group
management table is used to hold the number of logical extents that
constitute a corresponding extent group.
Next, the group management unit 1354 determines whether the
detected number Ne of logical extents exceeds a threshold Nth (step
S104). The threshold Nth is a reference value for determining
whether the specified extent group has grown enormous. In the
modification, the threshold Nth is set to a constant ratio, for
example, 1/2, of the maximum number of extents that can be arranged
in the upper tier (high-speed storage device 11). However, the
threshold Nth may be set to another value.
If Ne does not exceed Nth (No in step S104), the group management
unit 1354 determines that it is not necessary to regroup the
specified extent group. In this case, the group management unit
1354 completes the regrouping processing, and proceeds to step S3
of FIG. 8.
In contrast, if Ne exceeds Nth (Yes in step S104), the group
management unit 1354 executes three preprocesses (first to third
preprocesses) for regrouping the specified extent group, as
described below. First, the group management unit 1354 executes a
first preprocess to detect a pair of logical extents (a combination
of second and third logical extents) that have a minimum degree of
linkage (more specifically, a minimum degree of linkage other than
0) in the specified extent group (step S105). Step S105 will now be
described in detail.
First, the group management unit 1354 specifies all logical extents
in the specified extent group, based on the extent management table
1332. Next, the group management unit 1354 acquires, from the link
management table 1333, the degrees of linkage of respective pairs
of successively accessed logical extents included in the specified
logical extents. The group management unit 1354 detects a minimum
degree of linkage in the acquired degrees of linkage. Thus, the
group management unit 1354 detects a pair of logical extents that
have the minimum degree of linkage.
FIG. 23 shows a configuration example of an extent group GR1 and
examples of linkage degrees of respective pairs of successively
accessed logical extents included in extent group GR1, along with
an example of the link management table 1333, which examples are
obtained when extent group GR1 is specified as an expanded extent
group. In the examples of FIG. 23, it is assumed for simplification
of the description that extent group GR1 includes six logical
extents A, B, C, D, E and F (Ne=6), and Nth is 5. However, in
general, Ne and Nth are sufficiently greater than these values.
In FIG. 23, the arrows that connect logical extent A, B, C, D, E
and F in this order indicate the order of access. Therefore, the
preceding and succeeding link extents of, for example, logical
extent C are logical extents B and D, respectively. In FIG. 23, the
degrees of linkage (A, B) [=(B, A)], (B, C) [=(C, B)], (C, D) [=(D,
C)], (D, E) [=(E, D)] and (E, F) [=(F, E)] of the respective pairs
of adjacent logical extents in extent group GR1 are 50, 132, 5, 37
and 82, respectively. These degrees of linkage are reflected in the
link management table 1333 as shown by arrow 230. In the example of
FIG. 23, 5 is detected as the minimum degree of linkage.
Next, the group management unit 1354 executes a second preprocess
to normalize all degrees of linkage (more specifically, all degrees
of linkage other than 0) in the link management table 1333, using
the detected minimum degree of linkage (step S106). This
normalization means dividing each of all degrees of linkage in the
link management table 1333 by the detected minimum degree of
linkage. In FIG. 23, the minimum degree of linkage is the degree of
linkage (C, D) [=(D, C)], namely, 5.
FIG. 24 shows, for comparison, examples of the link management
table 1333 obtained before and after the second preprocess
(normalization). In FIG. 24, the link management table 1333 before
normalization is shown on the bottom side of arrow 240, and the
link management table 1333 after normalization is shown on the tip
side of arrow 240. The contents of the link management table 1333
before normalization coincides with that of the link management
table 1333 shown in FIG. 23. The minimum degree of linkage (C, D)
[=(D, C)] in the link management table 1333 is changed by the
normalization from 5 to 1 as shown in FIG. 24.
Next, the group management unit 1354 performs the third preprocess
to replace the normalized minimum degree of linkage (namely, 1) in
the link management table 1333 with 0 that indicates no linkage
(step S107). The linkage degree of 0 is equal to the value
expressed as a blank as mentioned above. By this replacement, the
linkage of a pair of logical extents having the minimum linkage of
1 is canceled.
FIG. 25 shows, for comparison, examples of the link management
table 1333 obtained before and after the third preprocess
(replacement with 0). In FIG. 25, the link management table 1333
before the replacement with 0 is shown on the bottom side of arrow
250, and the link management table 1333 after the replacement with
0 is shown on the tip side of arrow 250.
Next, the group management unit 1354 regroups all extents in the
specified extent group to reflect the above-mentioned replacement
with the linkage degree of (that is, to cancel the linkage
relationship between the pair of logical extents having the degree
of linkage thereof replaced with 0) (step S108). That is, the group
management unit 1354 divides the specified extent group (second
extent group) into an extent group (third extent group) including
one (second logical extent) of the pair of logical extents having
the degree of linkage thereof replaced with 0, and an extent group
(fourth extent group) including the other (third logical extent) of
the pair of logical extents, based on the extent management table
1332 and the link management table 1333.
In the modification, the group management unit 1354 imparts a new
extent group number, which is currently not used, to an extent
group including the preceding one (hereinafter, referred to as a
preceding extent) of the pair of logical extents having the degree
of linkage thereof replaced with 0. Further, the group management
unit 1354 imparts the extent group number of the original extent
group (namely, the specified extent group) to an extent group
including the succeeding one (hereinafter, referred to as a
succeeding extent) of the pair of logical extents having the degree
of linkage thereof replaced with 0. However, this may be modified
in an opposite way.
In the regrouping (step S108), the group management unit 1354
updates the extent management table 1332 as below. First, the group
management unit 1354 updates the contents of the EGN field and the
SLE field in an entry of the extent management table 1332
associated with the preceding extent, to the above-mentioned new
extent number and -1, respectively. The group management unit 1354
also updates, to -1, the contents of the PLE field in an entry of
the extent management table 1332 associated with the succeeding
extent.
After executing the regrouping (step S108), the group management
unit 1354 completes the regrouping processing according to the
flowchart of FIG. 22. Subsequently, in the modification, step S3 in
the flowchart of FIG. 8 is performed. Alternatively, the regrouping
processing may be performed at a time other than immediately before
step S3, that is, for example, immediately after step S3.
FIG. 26 shows an example of the link management table 1333 obtained
before the regrouping (i.e., immediately after the third
preprocess), and shows, for comparison, examples of extent groups
obtained immediately before and after the regrouping. In FIG. 26,
the link management table 1333 before the regrouping is shown on
the bottom side of arrow 261. As is evident from the above
description of step S108, the link management table 1333 is not
updated in the regrouping. That is, the link management table 1333
does not change before and after the regrouping. Therefore, the
link management table 1333 shown in FIG. 26 also shows the state
assumed after the regrouping. In FIG. 26, the configuration of
extent group GR1 before the regrouping is shown on the tip side of
arrow 261 and the bottom side of arrow 262. Extent group GR1 before
the regrouping, shown in FIG. 26, includes logical extents A, B, C,
D, E and F, as is also clear from FIG. 23.
The degree of linkage of a pair of logical extents C and D in
extent group GR1 before the regrouping is already changed to 0 by
the third preprocess (step S107). Therefore, the tiering controller
1355 cancels the linkage of logical extents C and D. After that,
the tiering controllers 1355 excludes, from extent group GR1,
logical extents C, A and B (namely, logical extent C and logical
extents A and B that have a direct or indirect linkage with logical
extent C), and makes them belong to new extent group GRa. That is,
the tiering controller 1355 regroups logical extents A, B, C, D, E
and F in extent group GR1 into new extent group GRa including
logical extents A, B and C, and reduced extent group GR1 including
logical extents D, E and F, as is indicated by arrow 262 in FIG. 26
(step S108).
The at least one embodiment described above can make data transfer
between tiers more efficient.
While certain embodiments have been described, these embodiments
have been presented by way of example only, and are not intended to
limit the scope of the inventions. Indeed, the novel embodiments
described herein may be embodied in a variety of other forms;
furthermore, various omissions, substitutions and changes in the
form of the embodiments described herein may be made without
departing from the spirit of the inventions. The accompanying
claims and their equivalents are intended to cover such forms or
modifications as would fall within the scope and spirit of the
inventions.
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